Characterizing the level of primordial non-Gaussianity (PNG) in the initial conditions for structure formation is one of the most promising ways to test inflation and differentiate among different scenarios. The scale-dependent imprint of PNG on the large-scale clustering of galaxies and quasars has already been used to place significant constraints on the level of PNG in our observed Universe. Such measurements depend upon an accurate and robust theory for how PNG affects the bias of galactic halos relative to the underlying matter density field. We improve upon previous work by employing a more general analytical method - the path-integral extension of the excursion set formalism - which is able to account for the non-Markovianity caused by PNG in the random-walk model used to identify halos in the initial density field. This non-Markovianity encodes information about environmental effects on halo formation which have so far not been taken into account in analytical bias calculations. We compute both scale-dependent and -independent corrections to the halo bias, along the way presenting an expression for the conditional collapsed fraction for the first time, and a new expression for the conditional halo mass function. To leading order in our perturbative calculation, we recover the halo bias results of Desjacques et. al. (2011), including the new scale-dependent correction reported there. However, we show that the non-Markovian dynamics from PNG can lead to marked differences in halo bias when next-to-leading order terms are included. We quantify these differences here.
We study the impact of primordial non-Gaussianity generated during inflation on the bias of halos using excursion set theory. We recapture the familiar result that the bias scales as $k^{-2}$ on large scales but explicitly identify the approximations that go into this conclusion and the corrections to it. We solve the more complicated problem of non-spherical halos, for which the collapse threshold is scale dependent.
We use stellar population synthesis modeling to analyze the host galaxy properties of a sample of 33 UV-selected, narrow-lined active galactic nuclei (AGNs) at z ~ 2 - 3. In order to quantify the contribution of AGN emission to host galaxy broadband spectral energy distributions (SEDs), we use the subsample of 11 AGNs with photometric coverage spanning from rest-frame UV through near-IR wavelengths. Modeling the SEDs of these objects with a linear combination of stellar population and AGN templates, we infer the effect of the AGN on derived stellar population parameters. We also estimate the typical bias in derived stellar populations for AGNs lacking rest-frame near-IR wavelength coverage, and develop a method for inferring the true host galaxy properties. We compare AGN host galaxy properties to those of a sample of UV-selected, star-forming non-AGNs in the same redshift range, including a subsample carefully matched in stellar mass. Although the AGNs have higher masses and SFRs than the full non-active sample, their stellar population properties are consistent with those of the mass-selected sample, suggesting that the presence of an AGN is not connected with the cessation of star-formation activity in star-forming galaxies at z ~ 2 - 3. We suggest that a correlation between M_BH and galaxy stellar mass is already in place at this epoch. Assuming a roughly constant Eddington ratio for AGNs at all stellar masses, we are unable to detect the AGNs in low-mass galaxies because they are simply too faint.
Double radio relics in galaxy clusters are rare phenomena that trace shocks in the outskirts of merging galaxy clusters. We have carried out a spectral and polarization study of the spectacular double relics in the galaxy cluster A3376 using the Giant Metrewave Radio Telescope at 150 and 325 MHz and the Very Large Array at 1400 MHz. The polarization study at 1400 MHz reveals a high degree of polarization (~30%) and aligned magnetic field vectors (not corrected for Faraday rotation) in the eastern relic. A highly polarized (>60%) filamentary radio source of size ~300 kpc near the eastern relic and north of the bent-jet radio galaxy is detected for the first time. The western relic is less polarized and does not show aligned magnetic field vectors. The distribution of spectral indices between 325 and 1400 MHz over the radio relics show steepening from the outer to the inner edges of the relics. The spectral indices of the eastern and the western relics imply Mach numbers in the range 2.2 to 3.3. Remarkable features such as the inward filament extending from the eastern relic, the highly polarized filament, the complex polarization properties of the western relic and the separation of the BCG from the ICM by a distance >900 kpc are noticed in the cluster. A comparison with simulated cluster mergers is required to understand the complex properties of the double relics in the context of the merger in A3376. An upper limit (log(P(1.4GHz) W/Hz < 23.0) on the strength of a Mpc size radio halo in A3376 is estimated.
We present the results of a visual search for galaxy-scale gravitational lenses in ~7 square degrees of Hubble Space Telescope (HST) images. The dataset comprises the whole imaging data ever taken with the Advanced Camera for Surveys (ACS) in the filter F814W (I-band) up to August 31st, 2011, i.e. 6.03 square degrees excluding the field of the Cosmic Evolution Survey (COSMOS). In addition, we have searched for lenses in the whole Wide Field Camera 3 (WFC3) near-IR imaging dataset in all filters 1.01 square degree up to the same date. Our primary goal is to provide a sample of lenses with a broad range of different morphologies and lens-source brightness contrast in order to design and train future automated lens finders in view of all-sky surveys. Our criteria to select lenses are purely morphological as we do not use any color or redshift information. The final candidate selection is very conservative hence leading to a nearly pure but incomplete sample. We find 49 new lens candidates: 40 in the ACS images and 9 in the WFC3 images. Out of these, 16 candidates are secure lenses owe to their highly recognizable morphology, 21 more are very good candidates, and 12 more have morphologies compatible with gravitational lensing. The imaging dataset is heterogeneous in depth and spans a broad range of galactic latitudes. It is therefore insensitive to cosmic variance and allows to estimate the number of galaxy-scale strong lenses on the sky for a putative survey depth. Because of the incompleteness of the sample, the estimated lensing rates should be taken as lower limits. Using these, we anticipate that a 15000 square degrees space survey such as Euclid will find at least 60000 galaxy-scale strong lenses down to a limiting AB magnitude of I=24.5 (10-sigma) or I=25.8 (3-sigma).
We exploit the SDSS galaxy groups catalogue of Yang et al. to study how the gas-phase metallicities of star-forming galaxies depend on environment. We find that satellite and central galaxies follow a qualitatively similar stellar mass (M_*) - gas-phase metallicity relation. Satellites, though, have higher gas-phase metallicities than equally massive centrals, and this difference increases with decreasing M_*. We also find that the gas-phase metallicity of satellites increases with halo mass at fixed stellar mass. This increment is more pronounced for less massive galaxies. We also show that low mass satellite galaxies have higher gas-phase metallicities than central galaxies of the same stellar metallicity. This difference becomes negligible for more massive galaxies of roughly solar metallicity. We demonstrate that the observed differences in gas-phase metallicity between centrals and satellites at fixed M_* are not a consequence of stellar mass stripping (advocated by Pasquali et al. in order to explain similar differences but in stellar metallicity), nor to the past star formation history of these galaxies as quantified by their surface mass density or gas mass fraction. Rather, we argue that these trends probably originate from a combination of three environmental effects: (i) strangulation, which prevents satellite galaxies from accreting new, low metallicity gas which would otherwise dilute their ISM, (ii) ram-pressure stripping of the outer gas disk, thereby inhibiting radial inflows of low-metallicity gas, and (iii) external pressure provided by the hot gas of the host halo which prevents metal-enriched outflows from escaping the galaxies. [abridged]
We describe a model of dark matter halo abundances and clustering which combines the two most widely used approaches to this problem: that based on peaks and the other based on excursion sets. Our approach can be thought of as addressing the cloud-in-cloud problem for peaks and/or modifying the excursion set approach so that it averages over a special subset, rather than all possible walks. In this respect, it seeks to account for correlations between steps in the walk as well as correlations between walks. We first show how the excursion set and peaks models can be written in the same formalism, and then use this correspondence to write our combined excursion set peaks model. We then give simple expressions for the mass function and bias, showing that even the linear halo bias factor is predicted to have a scale dependence as a consequence of the nonlocality associated with the peak constraint. At large masses, our model has little or no need to rescale the variable delta_c from the value associated with spherical collapse, and suggests a simple explanation for why the linear halo bias factor appears to lie above that based on the peak-background split at high masses when such a rescaling is assumed. Although we have concentrated on peaks, our analysis is more generally applicable to other traditionally single-scale analyses of large-scale structure.
We argue that from observations alone, only the transverse power spectrum $C_\ell(z_1,z_2)$ and the corresponding correlation function $\xi(\theta,z_1,z_2)$ can be measured and that these contain the full three dimensional information. We determine the two point galaxy correlation function at linear order in perturbation theory. Redshift space distortions are taken into account for arbitrary angular and redshift separations. We discuss the shape of the longitudinal and the transversal correlation functions which are very different from each other and from their real space counterpart. We then go on and suggest how to measure both, the Hubble parameter, $H(z)$, and the angular diameter distance, $D_A(z)$, separately from these correlation functions and perform an Alcock-Paczynski test.
(Abridged) We study the polarisation properties, magnetic field strength, and synchrotron emission scale-height of Milky-Way-like galaxies in comparison with other spiral galaxies. We use our 3D-emission model of the Milky Way Galaxy for viewing the Milky Way from outside at various inclinations as spiral galaxies are observed. When seen edge-on the synchrotron emission from the Milky Way has an exponential scale-height of about 0.74 kpc, which is much smaller than the values obtained from previous models. We find that current analysis methods overestimate the scale-height of synchrotron emission of galaxies by about 10% at an inclination of 80 degree and about 40% at an inclination of 70 degree because of contamination from the disk. The observed RMs for face-on galaxies derived from high-frequency polarisation measurements approximate to the Faraday depths (FDs) when scaled by a factor of two. For edge-on galaxies, the observed RMs are indicative of the orientation of the large-scale magnetic field, but are not well related with the FDs. Assuming energy equipartition between the magnetic field and particles for the Milky Way results in an average magnetic-field strength, which is about two times larger than the intrinsic value for a K factor of 100. The number distribution of the integrated polarisation percentages of a large sample of unresolved Milky-Way-like galaxies peaks at about 4.2% at 4.8 GHz and at about 0.8% at 1.4GHz. Integrated polarisation angles rotated by 90 degree align very well with the position angles of the major axes, implying that unresolved galaxies do not have intrinsic RMs.
When searching for populations of rare and/or weak signals in noisy data, it is common to use a detection threshold to remove marginal events which are unlikely to be the signals of interest; or a detector might have limited sensitivity, causing it to not detect some of the population. In both cases a selection of data has occurred, which can potentially bias any inferences drawn from the remaining data, and this effect must be corrected for. We show how the selection bias is naturally avoided by using the full information from the search, considering both the selected data and our ignorance of the data that are thrown away, and considering all relevant signal and noise models. This approach produces unbiased estimates of parameters even in the presence of false alarms and incomplete data.
We perform cosmological perturbation theory in Hassan-Rosen bimetric gravity for general homogeneous and isotropic backgrounds. In the de Sitter approximation, we obtain decoupled sets of massless and massive scalar gravitational fluctuations. Matter perturbations then evolve like in Einstein gravity. We perturb the future de Sitter regime by the ratio of matter to dark energy, producing quasi-de Sitter space. In this more general setting the massive and massless fluctuations mix. We argue that in the quasi-de Sitter regime, the growth of structure in bimetric gravity differs from that of Einstein gravity.
Gamma Ray Burst prompt emission is believed to originate from electrons accelerated in a highly relativistic outflow. "Internal shocks" due to collisions between shells ejected by the central engine is a leading candidate for electron acceleration. While synchrotron radiation is generally invoked to interpret prompt gamma-ray emission within the internal shock model, synchrotron self-Compton (SSC) is also considered as a possible candidate of radiation mechanism. In this case, one would expect a synchrotron emission component at low energies, and the naked-eye GRB 080319B has been considered as such an example. In the view that the gamma-ray lightcurve of GRB 080319B is much more variable than its optical counterpart, in this paper we study the relative variability between the synchrotron and SSC components. We develop a "top-down" formalism by using observed quantities to infer physical parameters, and subsequently to study the temporal structure of synchrotron and SSC components of a GRB. We complement the formalism with a "bottom-up" approach where the synchrotron and SSC lightcurves are calculated through a Monte-Carlo simulations of the internal shock model. Both approaches lead to the same conclusion. Small variations in the synchrotron lightcurve can be only moderately amplified in the SSC lightcurve. The SSC model therefore cannot adequately interpret the gamma-ray emission properties of GRB 080319B.
Links to: arXiv, form interface, find, astro-ph, recent, 1206, contact, help (Access key information)
(Abridged) We present measurements of the velocity dispersion profile (VDP) for different masses of galaxy groups, using ~16,000 groups selected from the final data release of the SDSS by Yang et al (2007). We divide the groups into subsamples according to the stellar mass of their central galaxy, and for each subsample we estimate the redshift-space cross-correlation function (CCF) with respect to a reference sample, xi(r_p,pi), as well as the projected CCF, w_p(r_p). An NFW profile plus a biased version of the linear mass autocorrelation function can well describe the observed w_p(r_p), providing an accurate determination of the real-space CCF xi(r). The one-dimensional VDP is extracted from the redshift distortion in xi(r_p,pi), by comparing xi(r_p,pi) with xi(r). We find that the velocity dispersion (VD) within the virial radius (R_200) shows a roughly flat profile, with a slight increase at <~ 0.3 R_200. The average VD within R_200, sigma_v, is a strongly increasing function of central galaxy mass, ranging from ~130km/s at M*~3x10^10 M_sun, up to ~650km/s at M*~5x10^11 M_sun. We extend our analysis to N-body simulations with the LCDM cosmology but different density fluctuation amplitudes, sigma_8. We apply the abundance matching model to assign a stellar mass to the central subhalos. We measure the VDP for the halos and compare the results to the data. We show that the sigma_v-M* relation provides stringent constraints on both sigma_8 and sigma_ms, the dispersion in log(M*) of central galaxies at fixed halo mass. Our data suggests sigma_8=0.86+/-0.03 and sigma_ms=0.16+/-0.03. The slightly higher sigma_8 compared to the WMAP7 result might be due to a smaller matter density parameter assumed in our simulations. Our sigma_v measurements also provide a direct measure of the halo masses, agreeing well with the results from the galaxy-galaxy lensing analysis by Mandelbaum et al. (2006).
We study the linear and nonlinear structure formation in the dilaton and symmetron modified gravity models using a generic parameterisation which describes a large class of scenarios using only a few parameters. For this we have modified the $N$-body code {\tt ECOSMOG} to perform a set of 110 simulations for different models and parameter values, including the default $\Lambda$CDM. These simulations enable us to explore a large portion of the parameter space. We have studied the effects of modified gravity on the matter power spectrum and mass function, and found rich and interesting phenomenology. The results reveal the qualitative behaviour of the models, and provide guidance for future more detailed studies.
Satellite galaxies in groups and clusters are more likely to have low star formation rates (SFR) and lie on the `red-sequence' than central (`field') galaxies. Using galaxy group/cluster catalogs from the Sloan Digital Sky Survey Data Release 7, together with a high-resolution, cosmological N-body simulation to track satellite orbits, we examine the star formation histories and quenching timescales of satellites of Mstar > 5 x 10^9 Msol at z ~ 0. We first explore satellite infall histories: group preprocessing and ejected orbits are critical aspects of satellite evolution, and properly accounting for these, satellite infall typically occurred at z ~ 0.5, or ~5 Gyr ago. To obtain accurate initial conditions for the SFRs of satellites at their time of first infall, we construct an empirical parametrization for the evolution of central galaxy SFRs. With this, we constrain empirically the amount and efficiency of satellite quenching as a function of satellite and host halo mass, finding that satellite quenching is the dominant process for building up all quiescent galaxies at Mstar < 10^10 Msol. We then constrain satellite star formation histories, finding a `delayed-then-rapid' quenching scenario: satellite SFRs evolve unaffected for 2 - 4 Gyr after infall, after which star formation quenches rapidly, with an e-folding time of < 0.8 Gyr. These quenching timescales are shorter for more massive satellites but do not depend on host halo mass: the observed increase in satellite quiescent fraction with halo mass arises simply because of group preprocessing, which is responsible for up to half of quenched satellites in massive clusters. Because of the long time delay before quenching starts, satellites experience significant stellar mass growth after infall, nearly identical to central galaxies. This fact is a key reason for the success of the subhalo abundance matching technique.
We demonstrate that dwarf galaxies (10^7 < M_stellar < 10^9 Msun) with no active star formation are extremely rare (<0.06%) in the field. Our sample is based on the NASA-Sloan Atlas which is a re-analysis of the Sloan Digital Sky Survey Data Release 8. We examine the relative number of quenched versus star forming dwarf galaxies, defining quenched galaxies as having no Halpha emission (EW_Halpha < 2 AA) and a strong 4000AA-break. The fraction of quenched dwarf galaxies decreases rapidly with increasing distance from a massive host, leveling off for distances beyond 1.5 Mpc. We define galaxies beyond 1.5 Mpc of a massive host galaxy to be in the field. We demonstrate that there is a stellar mass threshold of M_stellar < 1.0x10^9 Msun below which quenched galaxies do not exist in the field. Below this threshold, we find that none of the 2951 field dwarf galaxies are quenched; all field dwarf galaxies show evidence for recent star formation. Correcting for volume effects, this corresponds to a 1-sigma upper limit on the quenched fraction of 0.06%. In more dense environments, quenched galaxies account for 23% of the dwarf population over the same stellar mass range. The majority of quenched dwarf galaxies (often classified as dwarf elliptical galaxies) are within 2 virial radii of a massive galaxy, and only a few percent of quenched dwarf galaxies exist beyond 4 virial radii. Thus, for galaxies with stellar mass less than 1.0x10^9 Msun, ending star-formation requires the presence of a more massive neighbor, providing a stringent constraint on models of star formation feedback.
Recent deep Hubble Space Telescope WFC3 imaging suggests that a majority of compact quiescent massive galaxies at z~2 may contain disks. To investigate this claim, we have compared the ellipticity distribution of 31 carefully selected high-redshift massive quiescent compact galaxies to a set of mass-selected ellipticity and Sersic index distributions obtained from 2D structural fits to ~40,000$ nearby galaxies from the Sloan Digital Sky Survey. A Kolmogorov-Smirnov test shows that the distribution of ellipticities for the high-redshift galaxies is consistent with the ellipticity distribution of a similarly chosen sample of massive early-type galaxies. However the distribution of Sersic indices for the high-redshift sample is inconsistent with that of local early-type galaxies, and instead resembles that of local disk-dominated populations. The mismatch between the properties of high-redshift compact galaxies and those of both local early-type and disk-dominated systems leads us to conclude that the basic structures of high-redshift compact galaxies probably do not closely resemble those of any single local galaxy population. Any galaxy population analog to the high-redshift compact galaxies that exists at the current epoch is either a mix of different types of galaxies, or possibly a unique class of objects on their own.
Quasars with redshifts greater than four are rare, and can provide us important helps in probing the nature of the early universe. Here we report the discovery of six new quasars with $i$-band magnitudes brighter than 19.5 and redshifts between 2.4 and 4.6 from the spectroscopic observations made with the YFOSC instrument of the Lijiang 2.4m telescope in February, 2012. These six quasars are in the list of high redshift ($z>3.6$) quasar candidates selected by using our proposed J-K/i-Y criterion and the photometric redshift estimations from the SDSS optical and UKIDSS near-IR photometric data. Nine candidates were observed by YFOSC, and five among six new quasars were identified as $z>3.6$ quasars. One of the other three objects was identified as a star and the rest two were unidentified due to the lower signal-to-noise ratio of their spectra. This is the first time to discover quasars with redshifts greater than four with a telescope in China. Thanks to the Chinese Telescope Access Program (TAP), the redshift of 4.6 for one of these new quasars was confirmed by the MMT Red Channel spectroscopy. The continuum and emission line properties of these six quasars, as well as their central black hole masses and Eddington ratios, were obtained.
Using the Subaru 8.2m Telescope with an IRCS Echelle spectrograph, we obtained high-resolution (R=10,000) near-infrared (1.01-1.38 \mu m) spectra of images A and B of the gravitationally lensed QSO B1422+231 (z=3.628) consisting of four known lensed images. We detected MgII absorption lines at z=3.54, which show a large variance of column densities (~ 0.3 dex) and velocities (~ 10 km/s) between the sightlines A and B with a projected separation of only 8.4h_{70}^{-1} pc at the redshift. This is the smallest spatial structure of the high-z gas clouds ever detected after Rauch et al. found a 20-pc scale structure for the same z=3.54 absorption system using optical spectra of images A and C. The observed systematic variances imply that the system is an expanding shell as originally suggested by Rauch et al. By combining the data for three sightlines, we managed to constrain the radius and expansion velocity of the shell (~ 50-100 pc, 130 km/s), concluding that the shell is truly a supernova remnant (SNR) rather than other types of shell objects, such as a giant HII region. We also detected strong FeII absorption lines for this system, but with much broader Doppler width than that of \alpha-element lines. We suggest that this FeII absorption line originates in a localized FeII-rich gas cloud that is not completely mixed with plowed ambient interstellar gas clouds showing other \alpha-element low-ion absorption lines. Along with the Fe richness, we conclude that the SNR is produced by an SNIa explosion.
Galaxy diversification proceeds by transforming events like accretion, interaction or mergers. These explain the formation and evolution of galaxies that can now be described with many observables. Multivariate analyses are the obvious tools to tackle the datasets and understand the differences between different kinds of objects. However, depending on the method used, redundancies, incompatibilities or subjective choices of the parameters can void the usefulness of such analyses. The behaviour of the available parameters should be analysed before an objective reduction of dimensionality and subsequent clustering analyses can be undertaken, especially in an evolutionary context. We study a sample of 424 early-type galaxies described by 25 parameters, ten of which are Lick indices, to identify the most structuring parameters and determine an evolutionary classification of these objects. Four independent statistical methods are used to investigate the discriminant properties of the observables and the partitioning of the 424 galaxies: Principal Component Analysis, K-means cluster analysis, Minimum Contradiction Analysis and Cladistics. (abridged)
Possibility of gravitational repulsion in General Relativity is discussed and astronomical data in favor of cosmological acceleration are described. The problem of vacuum energy is emphasized and possible ways of its solution are indicated. The main attention is payed to adjustment mechanism which in principle could compensate originally huge vacuum energy down to cosmologically acceptable value and to solve the coincidence problem of a close magnitudes of the non-compensated remnants of vacuum energy and the energy density of the universe at the present time. Finally possible modifications of gravity at large scales which could induce accelerated cosmological expansion are considered.
A possible solution to the small scale problems of the cold dark matter (CDM) scenario is that the dark matter consists of two components, a cold and a warm one. We perform a set of high resolution simulations of the Milky Way halo varying the mass of the WDM particle ($m_{\rm WDM}$) and the cosmic dark matter mass fraction in the WDM component ($\bar{f}_{\rm W}$). The scaling ansatz introduced in combined analysis of LHC and astroparticle searches postulates that the relative contribution of each dark matter component is the same locally as on average in the Universe (e.g. $f_{\rm W,\odot} = \bar{f}_{\rm W}$). Here we find however, that the normalised local WDM fraction ($f_{\rm W,\odot}$ / $\bar{f}_{\rm W}$) depends strongly on $m_{\rm WDM}$ for $m_{\rm WDM} <$ 1 keV. Using the scaling ansatz can therefore introduce significant errors into the interpretation of dark matter searches. To correct this issue a simple formula that fits the local dark matter densities of each component is provided.
We present Hubble Space Telescope imaging and spectroscopy for the extended high-ionization cloud known as Hanny's Voorwerp, near the spiral galaxy IC 2497. WFC3 images show complex dust absorption near the nucleus of IC 2497. STIS spectra show a type 2 Seyfert AGN of rather low luminosity. The ionization parameter log U = -3.5 is in accord with its weak X-ray emission. We find no high-ionization gas near the nucleus, adding to evidence that the AGN is currently at low radiative output (perhaps now dominated by kinetic energy). The nucleus is accompanied by an expanding ring of ionized gas 500 pc in projected diameter on the side opposite Hanny's Voorwerp, with Doppler offset 300 km/s from the nucleus (kinematic age < 7 x10^5 years). [O III] and H-alpha + [N II] images show fine structure in Hanny's Voorwerp, with limb-brightened sections and small areas where H-alpha is strong. We identify these as regions ionized by recent star formation, in contrast to the AGN ionization of the entire cloud. These candidate "normal" H II regions contain blue continuum objects, whose colors are consistent with young stellar populations; they appear only in a 2-kpc region toward IC 2497 in projection. The ionization-sensitive ratio [O III]/H-alpha shows no discernible pattern near the prominent "hole" in the ionized gas. The independence of ionization and surface brightness suggests that substantial spatial structure remains unresolved, to such an extent that the surface brightness sample the number of denser filaments rather than the characteristic density in emission regions. These results fit with our picture of an ionization echo from an AGN whose ionizing luminosity has dropped by a factor > 100 (and possibly much more) within the last 1-2 x 10^5 years; we suggest a sequence of events and discuss implications of such rapid fluctuations for AGN demographics. (Abridged)
Galaxy structure and morphology is nearly always studied using the light originating from stars, however ideally one is interested in measuring structure using the stellar mass distribution. Not only does stellar mass trace out the underlying distribution of matter, it also minimises the effects of star formation and dust on the appearance and structure of a galaxy. We present in this paper a study of the stellar mass distributions and structures of galaxies at z<1 as found within the GOODS fields. We use pixel by pixel K-corrections to construct stellar mass and mass-to-light ratio maps of 560 galaxies of known morphology at magnitudes z_{850}<24. We measure structural and size parameters using these stellar mass maps, as well as on ACS BViz band imaging. This includes investigating the structural CAS-Gini-M_{20} parameters and half-light radius for each galaxy. We compare structural parameters and half-light radii in the ACS z_{850}-band and stellar mass maps, finding no systematic bias introduced by measuring galaxy sizes in z_{850}. We furthermore investigate relations between structural parameters in the ACS BViz bands and stellar mass maps, and compare our result to previous morphological studies. Combinations of various parameters in stellar mass generally reveal clear separations between early and late type morphologies, but cannot easily distinguish between star formation and dynamically disturbed systems. We also show that while ellipticals and early-type spirals have fairly constant CAS values at z<1 we find a tendency for late-type spiral and peculiar morphological types to have a higher A(M_{*}) at higher redshift. We argue that this, and the large fraction of peculiars that appear spiral-like in stellar mass maps, are possible evidence for either an active bulge formation in some late-type disks at z<1 or the presence of minor merger events.
This brief historical review highlights the early work of Hayashi and his associates on the thermal physics of star-forming clouds, as summarized in the temperature-density diagrams first presented by this group. Some of the more recent developments in this subject, including its application to understanding stellar masses and to understanding the formation of the first stars, are also briefly reviewed.
We present initial results from the CO survey toward high redshift galaxies using the Nobeyama 45m telescope. Using the new wide bandwidth spectrometer equipped with a two-beam SIS receiver, we have robust new detections of three high redshift (z=1.6-3.4) submillimeter galaxies (SXDF 1100.001, SDP9, and SDP17), one tentative detection (SDSS J160705+533558), and one non-detection (COSMOS-AzTEC1). The galaxies observed during the commissioning phase are sources with known spectroscopic redshifts from previous optical or from wide-band submm spectroscopy. The derived molecular gas mass and line widths from Gaussian fits are ~10^11 Msun and 430-530 km/s, which are consistent with previous CO observations of distant submm galaxies and quasars. The spectrometer that allows a maximum of 32 GHz instantaneous bandwidth will provide new science capabilities at the Nobeyama 45m telescope, allowing us to determine redshifts of bright submm selected galaxies without any prior redshift information.
We have modelled the inner surface brightness profiles of 39 alleged `core' galaxies with the core-Sersic model, and provide new physical parameters for the largest ever sample of `core' galaxies fit with this model. When present, additional nuclear components were simultaneously modelled and the typical rms scatter of the fits (out to ~10 arcsec) is 0.02 mag/arcsec^2. Model-independent estimates of each core's break radius are shown to agree with those from the core-Sersic model, and a comparison with the Nuker model is provided. We found an absence of cores in what amounts to 18% of the sample which are reclassified here as Sersic galaxies with low values of n (< ~ 4) and thus shallow inner profile slopes. In general, galaxies with n<3 and sigma < 183 km/s do not have depleted cores. We derive updated relations between core-Sersic break radii, their associated surface brightness, bulge luminosity, central velocity dispersion, and predicted black hole mass for galaxies with depleted cores. With the possible exception of NGC 584, we confirm that the inner negative logarithmic profile slopes gamma are < ~ 0.3 for the `core' galaxies, and 0 > gamma > -0.1 for six of these. Finally, the central stellar mass deficits are found to have values typically within a factor of 4 of the expected central black hole mass.
We construct axisymmetric mass models for dwarf spheroidal (dSph) galaxies in the Milky Way to obtain plausible limits on the non-spherical structure of their dark halos. This is motivated by the fact that the observed luminous parts of the dSphs are actually non-spherical and Cold Dark Matter (CDM) models predict non-spherical virialized dark halos. Our models consider velocity anisotropy of stars $\bar{v^2_R} / \bar{v^2_{\phi}}$, which can vary with the adopted cylindrical coordinates under the assumption $\bar{v^2_z}=\bar{v^2_R}$ for simplicity, and also include an inclination of the system as a fitting parameter to explain the observed line-of-sight velocity dispersion profile. Applying these models to six of the bright dSphs in the Milky Way, we find that the best-fitting cases for most of the dSphs yield oblate and flattened dark halos, irrespective of assumed density profiles in their central parts. We also find that the total mass of the dSphs enclosed within a spheroid with major-axis length of 300 pc varies from $10^6M_{\odot}$ to $10^7M_{\odot}$, contrary to the conclusion from spherical models. This suggests the importance of considering shapes of dark halos in mass models of the dSphs. It is also found that dark halos of the Galactic dSphs may be more flattened than N-body predictions, thereby implying our yet incomplete understanding of baryonic and/or non-baryonic dark matter physics in dwarf galaxy scales.
The relation between the ratio of infrared (IR) and ultraviolet (UV) flux densities (the infrared excess: IRX) and the slope of the UV spectrum (\beta) of galaxies plays a fundamental role in the evaluation of the dust attenuation of star forming galaxies especially at high redshifts. Many authors, however, pointed out that there is a significant dispersion and/or deviation from the originally proposed IRX-\beta relation depending on sample selection. We reexamined the IRX-\beta relation by measuring the far- and near-UV flux densities of the original sample galaxies with GALEX and AKARI imaging data, and constructed a revised formula. We found that the newly obtained IRX values were lower than the original relation because of the significant underestimation of the UV flux densities of the galaxies, caused by the small aperture of IUE, Further, since the original relation was based on IRAS data which covered a wavelength range of \lambda = 42--122\mum, using the data from AKARI which has wider wavelength coverage toward longer wavelengths, we obtained an appropriate IRX-\beta relation with total dust emission (TIR): \log(L_{\rm TIR}/L_{\rm FUV}) = \log [10^{0.4(3.06+1.58\beta)}-1] +0.22. This new relation is consistent with most of the preceding results for samples selected at optical and UV, though there is a significant scatter around it. We also found that even the quiescent class of IR galaxies follows this new relation, though luminous and ultraluminous IR galaxies distribute completely differently as well known before.
We consider models of accelerating Universe elaborated for Finsler like gravity theories constructed on tangent bundles to Lorentz manifolds. In the osculating approximation, certain locally anisotropic configurations are similar to those for f(R) gravity. This allows us to generalize a proposal (by Nojiri, Odintsov and Saez-Gomez, arXiv: 1108.0767) in order to reconstruct and compare two classes of Einstein-Finsler gravity, EFG, and f(R) gravity theories using modern cosmological data and realistic physical scenarios. We conclude that EFG provides inflation, acceleration and little rip evolution scenarios with realistic alternatives to standard Lambda CDM cosmology. The approach is based on a proof that there is a general decoupling property of gravitational field equations in EFG and modified theories which allows us to generate off-diagonal cosmological solutions.
We report the first two-dimensional mapping of the stellar population and non-stellar continua within the inner 180 pc (radius) of NGC 1068 at a spatial resolution of 8 pc, using integral field spectroscopy in the near-infrared. We have applied the technique of spectral synthesis to data obtained with the instrument NIFS and the adaptive optics module ALTAIR at the Gemini North Telescope. Two episodes of recent star formation are found to dominate the stellar population contribution: the first occurred 300 Myr ago, extending over most of the nuclear region; the second occurred just 30 Myr ago, in a ring-like structure at ~100 pc from the nucleus, where it is coincident with an expanding ring of H2 emission. Inside the ring, where a decrease in the stellar velocity dispersion is observed, the stellar population is dominated by the 300 Myr age component. In the inner 35 pc, the oldest age component (age > 2Gyr) dominates the mass, while the flux is dominated by black-body components with temperatures in the range 700 < T < 800 K which we attribute to the dusty torus. We also find some contribution from black-body and power-law components beyond the nucleus which we attribute to dust emission and scattered light.
We use numerical simulations to study the effects of the patchiness of a partly reionized intergalactic medium (IGM) on the observability of Ly-alpha emitters (LAEs) at high redshifts (z ~ 6). We present a new model that divides the Ly-alpha radiative transfer into a (circum-)galactic and an extragalactic (IGM) part, and investigate how the choice of intrinsic line model affects the IGM transmission results. We use our model to study the impact of neutral hydrogen on statistical observables such as the Ly-alpha restframe equivalent width (REW) distribution, the LAE luminosity function and the two-point correlation function. We find that if the observed changes in LAE luminosity functions and equivalent width distributions between z ~ 6 and z ~ 7 are to be explained by an increased IGM neutral fraction alone, we require an extremely late and rapid reionization scenario, where the Universe was ~ 40 % ionized at z = 7, ~ 50 % ionized at z = 6.5 and ~ 100 % ionized at z = 6. This is in conflict with other observations, suggesting that intrinsic LAE evolution at z > 6 cannot be completely neglected. We show how the two-point correlation function can provide more robust constraints once future observations obtain larger LAE samples, and provide predictions for the sample sizes needed to tell different reionization scenarios apart.
The cosmological origin of both dark and baryonic matter can be explained through a unified mechanism called hylogenesis where baryon and antibaryon number are divided between the visible sector and a GeV-scale hidden sector, while the Universe remains net baryon symmetric. The "missing" antibaryons, in the form of exotic hidden states, are the dark matter. We study model-building, cosmological, and phenomenological aspects of this scenario within the framework of supersymmetry, which naturally stabilizes the light hidden sector and electroweak mass scales. Inelastic dark matter scattering on visible matter destroys nucleons, and nucleon decay searches offer a novel avenue for the direct detection of the hidden antibaryonic dark matter sea.
We suggest that galileon theories should have an additional self-coupling of the fields to the trace of their own energy-momentum tensor. We explore the classical features of one such model, in flat 4D spacetime, with emphasis on solutions that are scalar analogues of gravitational geons. We discuss the stability of these scalar geons, and some of their possible signatures, including shock fronts.
We study perturbations around some cosmological backgrounds in the dRGT theory of massive gravity. We develop a general formalism to calculate the perturbations around any background. We derive the Lagrangian for fluctuations in the small scale limit, and for the open FRW solution we repeat the analysis around the full background. We find that the perturbations display similar properties: the longitudinal modes of the massive graviton are instantaneous at quadratic level, but they acquire a time-kinetic term at cubic order.
The ultracompact minihalos would be formed during the earlier epoch of cosmology. The dark matter annihilation within them is very strong due to the high density. The electron and positron with high energy from the dark matter annihilation can inverse Compton scatter (ICS) the background photons, such as CMB photons, into the higher energy. On the other hand, the synchrotron radiation can also be produced when they meet the magnetic field. In this paper, we study the signals from the UCMHs due to the dark matter annihilation into the radio, x-ray and {\gamma}-ray bands. We found that for the radio emission the UCMHs can provide one kinds of sources of the radio excess observed by ARCADE 2. But for these dark matter models, the x-ray signals due to the ICS effect and the {\gamma}-ray signals mainly due to the prompt emission from dark matter would excess the present observations, such as Fermi, COMPTEL and CHANDRA.
A vertical X-shaped structure was recently reported in the Galactic bulge. Here we present evidence of a similar X-shaped structure in the Shen et al. (2010) bar/boxy bulge model that simultaneously matches the stellar kinematics successfully. The X-shaped structure is found in the central region of our bar/boxy bulge model, and is qualitatively consistent with the observed one in many aspects. End-to-end separations of the X-shaped structure in the radial and vertical directions are roughly 3 kpc and 2 kpc, respectively. The X-shaped structure contains about 7% of light in the boxy bulge region, but it is significant enough to be identified in observations. An X-shaped structure naturally arises in the formation of bar/boxy bulges, and is mainly associated with orbits trapped around the vertically-extended x_1 family. Like the bar in our model, the X-shaped structure tilts away from the Sun--Galactic center line by 20 degrees. The X-shaped structure becomes increasingly symmetric about the disk plane, so the observed symmetry may indicate that it formed at least a few billion years ago. The existence of the vertical X-shaped structure suggests that the formation of the Milky Way bulge is shaped mainly by internal disk dynamical instabilities.
We derive a phenomenological expression that predicts the final mass of the black-hole remnant resulting from the merger of a generic binary system of black holes on quasi-circular orbits. Besides recovering the correct test-particle limit for extreme mass-ratio binaries, our formula reproduces well the results of all the numerical-relativity simulations published so far, both when applied at separations of a few gravitational radii, and when applied at separations of tens of thousands of gravitational radii. These validations make our formula a useful tool in a variety of contexts ranging from gravitational-wave physics to cosmology. As representative examples, we first illustrate how it can be used to decrease the phase error of the effective-one-body waveforms during the ringdown phase. Secondly, we show that, when combined with the recently computed self-force correction to the binding energy of nonspinning black-hole binaries, it provides an estimate of the energy emitted during the merger and ringdown. Finally, we use it to calculate the energy radiated in gravitational waves by massive black-hole binaries as a function of redshift, using different models for the seeds of the black-hole population.
We have conducted a systematic search of low-mass black holes (BHs) in active galactic nuclei (AGNs) with broad Halpha emission lines, aiming at building a homogeneous sample that is more complete than previous ones for fainter, less highly accreting sources. For this purpose, we developed a set of elaborate, automated selection procedures and applied it uniformly to the Fourth Data Release of the Sloan Digital Sky Survey. Special attention is given to AGN--galaxy spectral decomposition and emission-line deblending. We define a sample of 309 type 1 AGNs with BH masses in the range $8 \times 10^4$--$2 \times 10^6$ \msun (with a median of $1.2 \times 10^6$ solar mass), using the virial mass estimator based on the broad Halpha line. About half of our sample of low-mass BHs differs from that of Greene & Ho, with 61 of them discovered here for the first time. Our new sample picks up more AGNs with low accretion rates: the Eddington ratios of the present sample range from $<~0.01$ to ~1, with 30% below 0.1. This suggests that a significant fraction of low-mass BHs in the local Universe are accreting at low rates. The host galaxies of the low-mass BHs have luminosities similar to those of $L^*$ field galaxies, optical colors of Sbc spirals, and stellar spectral features consistent with a continuous star formation history with a mean stellar age of less than 1 Gyr.
In de Sitter spacetime there exists an absolute minimum for the mass of a spin-2 field set by the Higuchi bound m^2 \geq 2H^2. We generalize this bound to arbitrary spatially flat FRW geometries in the context of the recently proposed ghostfree models of Massive Gravity by performing a Hamiltonian analysis for cosmological perturbations. We find that the bound generically indicates that spatially flat FRW solutions in massive gravity, which exhibit a Vainshtein mechanism in the background as required by consistency with observations, imply that the helicity zero mode is a ghost. In contradistinction to previous works, the tension between the Higuchi bound and the Vainshtein mechanism is equally strong regardless of the equation of state for matter.
Type IIP (Plateau) Supernovae are the most commonly observed variety of core collapse events. They have been detected in a wide range of wavelengths from radio, through optical to X-rays. The standard picture of a type IIP supernova has the blastwave interacting with the progenitor's circumstellar matter to produce a hot region bounded by a forward and a reverse shock. This region is thought to be responsible for most of the X-ray and radio emission from these objects. Yet the origin of X-rays from these supernovae is not well understood quantitatively. The relative contributions of particle acceleration and magnetic field amplification in generating the X-ray and radio emission need to be determined. In this work we analyze archival Chandra observations of SN 2004dj, the nearest supernova since SN 1987A, along with published radio and optical information. We determine the pre-explosion mass loss rate, blastwave velocity, electron acceleration and magnetic field amplification efficiencies. We find that a greater fraction of the thermal energy goes into accelerating electrons than into amplifying magnetic fields. We conclude that the X-ray emission arises out of a combination of inverse Compton scattering by non-thermal electrons accelerated in the forward shock and thermal emission from supernova ejecta heated by the reverse shock.
We attempt an estimate for the distribution of the tensor mode fraction $r$ over the landscape of vacua in string theory. The dynamics of eternal inflation and quantum tunneling lead to a kind of democracy on the landscape, providing no bias towards large-field or small-field inflation regardless of the class of measure. The tensor mode fraction then follows the number frequency distributions of inflationary mechanisms of string theory over the landscape. We show that an estimate of the relative number frequencies for small-field vs large-field inflation, while unattainable on the whole landscape, may be within reach as a regional answer for warped Calabi-Yau flux compactifications of type IIB string theory.
Links to: arXiv, form interface, find, astro-ph, recent, 1206, contact, help (Access key information)
The zCOSMOS-bright 10k spectroscopic sample reveals a strong environmental dependence of close kinematic galaxy pair fractions in the redshift range 0.2 < z < 1. The fraction of close pairs is three times higher in the top density quartile than in the lowest one. This environmental variation in pair fractions will translate into merger fractions since merger timescales are shown, based on Millennium simulation catalogs, to be largely independent of environment. While galactic properties of close kinematic pairs (morphologies and star formation rates) may seem to be non-representative of an underlying galaxy population, they can be explained by taking into account well-known effects of environment, and changes caused by interactions. The latter is responsible for an increase of irregular galaxies in pairs by a factor of 50-75%, with a disproportionate increase in the number of irregular-irregular pairs (4-8 times), due to disturbance of about 15% of the disk galaxies in pairs. Another sign of interaction is an observed boost in specific star formation rate (factor 2-4) for the closest pairs. While significant for paired galaxies, this triggered star-formation due to interactions represents only about 5% of the integrated star-formation activity in our volume-limited sample. Although majority of close kinematic pairs are in dense environments, the effects of interactions appear to be strongest in the lower density environments. This may introduce strong biases into observational studies of mergers, especially those based on morphological criteria. Relative excess of post-starburst galaxies observed in paired galaxies (factor \sim2) as well as excess of AGNs (factor of over 2), linked with environmental dependence of the pair fractions could indicate that early phases of interactions and merging are plausible candidates for environmental quenching, observed in the global galaxy populations.
As part of the Panchromatic Hubble Andromeda Treasury (PHAT) multi-cycle program, we observed a 12' \times 6.5' area of the bulge of M31 with the WFC3/UVIS filters F275W and F336W. From these data we have assembled a sample of \sim4000 UV-bright, old stars, vastly larger than previously available. We use updated Padova stellar evolutionary tracks to classify these hot stars into three classes: Post-AGB stars (P-AGB), Post-Early AGB (PE-AGB) stars and AGB-manqu\'e stars. P-AGB stars are the end result of the asymptotic giant branch (AGB) phase and are expected in a wide range of stellar populations, whereas PE-AGB and AGB-manqu\'e (together referred to as the hot post-horizontal branch; HP-HB) stars are the result of insufficient envelope masses to allow a full AGB phase, and are expected to be particularly prominent at high helium or {\alpha} abundances when the mass loss on the RGB is high. Our data support previous claims that most UV-bright sources in the bulge are likely hot (extreme) horizontal branch stars (EHB) and their progeny. We construct the first radial profiles of these stellar populations, and show that they are highly centrally concentrated, even more so than the integrated UV or optical light. However, we find that this UV-bright population does not dominate the total UV luminosity at any radius, as we are detecting only the progeny of the EHB stars that are the likely source of the UVX. We calculate that only a few percent of MS stars in the central bulge can have gone through the HP-HB phase and that this percentage decreases strongly with distance from the center. We also find that the surface density of hot UV-bright stars has the same radial variation as that of low-mass X-ray binaries. We discuss age, metallicity, and abundance variations as possible explanations for the observed radial variation in the UV-bright population.
We report new, sensitive observations of two z ~ 3-3.5 FIR-luminous radio galaxies, 6C1909+72 and B3J2330+3927, in 12CO J=1-0 with the Karl Jansky VLA and at 100-500um using Herschel, alongside new and archival 12CO J=4-3 observations from IRAM PdBI. We introduce a new colour-colour diagnostic plot to constrain the redshifts of several distant, dusty galaxies in our target fields. A bright SMG near 6C1909+72 likely shares the same node or filament as the signpost AGN, but it is not detected in CO despite ~20,000 km/s of velocity coverage. Also in the 6C1909+72 field, a large, red dust feature spanning ~500 kpc is aligned with the radio jet. We suggest several processes by which metal-rich material may have been transported, favouring a collimated outflow reminiscent of the jet-oriented metal enrichment seen in local cluster environments. Our interferometric imaging reveals a gas-rich companion to B3J2330+3927; indeed, all bar one of the eight z >~ 2 radio galaxies (or companions) detected in CO provide some evidence that starburst activity in radio-loud AGN at high redshift is driven by the interaction of two or more gas-rich systems in which a significant mass of stars has already formed, rather than via steady accretion of cold gas from the cosmic web. We find that the CO Tb ratios in radio-loud AGN host galaxies are significantly higher than those seen in similarly intense starbursts where AGN activity is less pronounced. Our most extreme example, where L'(CO4-3)/L'(CO1-0) > 2.7, provides evidence that significant energy is being deposited rapidly into the molecular gas via X-rays and/or mechanical (`quasar-mode') feedback from the AGN, leading to a high degree of turbulence globally and a low optical depth in 12CO - feedback that may lead to the cessation of star formation on a timescale commensurate with that of the jet activity, <~10 Myr.
We present spectroscopic observations in the rest-frame optical and near- to mid-infrared wavelengths of four gravitationally lensed infrared (IR) luminous star-forming galaxies at redshift 1 < z < 3 from the LUCIFER instrument on the Large Binocular Telescope and the Infrared Spectrograph on Spitzer. The sample was selected to represent pure, actively star-forming systems, absent of active galactic nuclei. The large lensing magnifications result in high signal-to-noise spectra that can probe faint IR recombination lines, including Pa-alpha and Br-alpha at high redshifts. The sample was augmented by three lensed galaxies with similar suites of unpublished data and observations from the literature, resulting in the final sample of seven galaxies. We use the IR recombination lines in conjunction with H-alpha observations to probe the extinction, Av, of these systems, as well as testing star formation rate (SFR) indicators against the SFR measured by fitting spectral energy distributions to far-IR photometry. Our galaxies occupy a range of Av from ~0 to 5.9 mag, larger than previously known for a similar range of IR luminosities at these redshifts. Thus, estimates of SFR even at z ~ 2 must take careful count of extinction in the most IR luminous galaxies. We also measure extinction by comparing SFR estimates from optical emission lines with those from far-IR measurements. The comparison of results from these two independent methods indicates a large variety of dust distribution scenarios at 1 < z < 3. Without correcting for dust extinction, the H-alpha SFR indicator underestimates the SFR; the size of the necessary correction depends on the IR luminosity and dust distribution scenario. Individual SFR estimates based on the 6.2 micron PAH emission line luminosity do not show a systematic discrepancy with extinction, although a considerable, ~0.2 dex scatter is observed.
We introduce a method for constructing end-to-end mock galaxy catalogues using a semi-analytical model of galaxy formation, applied to the halo merger trees extracted from a cosmological N-body simulation. The mocks that we construct are lightcone catalogues, in which a galaxy is placed according to the epoch at which it first enters the past lightcone of the observer, and incorporate the evolution of galaxy properties with cosmic time. We determine the position between the snapshot outputs at which a galaxy enters the observer's lightcone by interpolation. As an application, we consider the effectiveness of the BzK colour selection technique, which was designed to isolate galaxies in the redshift interval 1.4<z<2.5. The mock catalogue is in reasonable agreement with the observed number counts of all BzK galaxies, as well as with the observed counts of the subsample of BzKs that are star-forming galaxies. We predict that over 75 per cent of the model galaxies with K_{AB}<=23, and 1.4<z<2.5, are selected by the BzK technique. Interloper galaxies, outside the intended redshift range, are predicted to dominate bright samples of BzK galaxies (i.e. with K_{AB}<=21). Fainter K-band cuts are necessary to reduce the predicted interloper fraction. We also show that shallow B-band photometry can lead to confusion in classifying BzK galaxies as being star-forming or passively evolving. Overall, we conclude that the BzK colour selection technique is capable of providing a sample of galaxies that is representative of the 1.4<z<2.5 galaxy population.
We present the Pan-STARRS1 discovery and light curves, and follow-up MMT and Gemini spectroscopy of an ultra-luminous supernova (ULSN; dubbed PS1-11bam) at a redshift of z=1.566 with a peak brightness of M_UV=-22.3 mag. PS1-11bam is one of the highest redshift spectroscopically-confirmed SNe known to date. The spectrum is characterized by broad absorption features typical of previous ULSNe (e.g., CII, SiIII), and by strong and narrow MgII and FeII absorption lines from the interstellar medium (ISM) of the host galaxy, confirmed by an [OII]3727 emission line at the same redshift. The equivalent widths of the FeII2600 and MgII2803 lines are in the top quartile of the quasar intervening absorption system distribution, but are weaker than those of gamma-ray burst intrinsic absorbers (i.e., GRB host galaxies). We also detect the host galaxy in pre-explosion Pan-STARRS1 data and find that its UV spectral energy distribution is best fit with a young stellar population age of tau~15-45 Myr and a stellar mass of M \sim (1.1-2.6)x10^9 M_sun (for Z=0.05-1 Z_sun). The star formation rate inferred from the UV continuum and [OII]3727 emission line is ~10 M_sun/yr, higher than in any previous ULSN host. PS1-11bam provides the first direct demonstration that ULSNe can serve as probes of the interstellar medium in distant galaxies. At the present, the depth and red sensitivity of PS1 are uniquely suited to finding such events at cosmologically interesting redshifts (z~1-2); the future combination of LSST and 30-m class telescopes promises to extend this technique to z~4.
(abridged) We present a clustering analysis of 370 high-confidence H-alpha emitters (HAEs) at z=2.23. The HAEs are detected in the Hi-Z Emission Line Survey (HiZELS), a large-area blank field 2.121um narrowband survey using the United Kingdom Infrared Telescope (UKIRT) Wide Field Camera (WFCAM). Averaging the two-point correlation function of HAEs in two ~1 degree scale fields (United Kingdom Infrared Deep Sky Survey/Ultra Deep Survey [UDS] and Cosmological Evolution Survey [COSMOS] fields) we find a clustering amplitude equivalent to a correlation length of r_0=3.7+/-0.3 Mpc/h for galaxies with star formation rates of >7 M_sun/yr. The data are well-fitted by the expected correlation function of Cold Dark Matter, scaled by a bias factor: omega_HAE=b^2 omega_DM where b=2.4^{+0.1}_{-0.2}. The corresponding 'characteristic' mass for the halos hosting HAEs is log(M_h/[M_sun/h])=11.7+/-0.1. Comparing to the latest semi-analytic GALFORM predictions for the evolution of HAEs in a LCDM cosmology, we find broad agreement with the observations, with GALFORM predicting a HAE correlation length of ~4 Mpc/h. Motivated by this agreement, we exploit the simulations to construct a parametric model of the halo occupation distribution (HOD) of HAEs, and use this to fit the observed clustering. Our best-fitting HOD can adequately reproduce the observed angular clustering of HAEs, yielding an effective halo mass and bias in agreement with that derived from the scaled omega_DM fit, but with the relatively small sample size the current data provide a poor constraint on the HOD. Our results support the broad picture that 'typical' (~L*) star-forming galaxies have been hosted by dark matter haloes with M_h<10^12 M_sun/h since z~2, but with a broad occupation distribution and clustering that is likely to be a strong function of luminosity.
We present a detailed analysis (including redshift tomography) of the cosmic dipoles in the Keck+VLT quasar absorber and in the Union2 SnIa samples. We show that the fine structure constant cosmic dipole obtained through the Keck+VLT quasar absorber sample at $4.1\sigma$ level, is anomalously aligned with the corresponding dark energy dipole obtained through the Union2 sample at $2\sigma$ level. The angular separation between the two dipole directions is $11.3^\circ \pm 11.8^\circ$. We use Monte Carlo simulations to find the probability of obtaining the observed dipole magnitudes with the observed alignment, in the context of an isotropic cosmological model with no correlation between dark energy and fine structure constant. We find that this probability is less than one part in $10^6$. We propose a simple physical model (extended topological quintessence) which naturally predicts spherical inhomogeneous distribution for both dark energy density and fine structure constant values. The model is based on the existence of a recently formed giant global monopole with Hubble scale core which also couples non-minimally to electromagnetism. Aligned dipole anisotropies would naturally emerge for an off-center observer for both the fine structure constant and for dark energy density. This model smoothly reduces to \lcdm for proper limits of its parameters.
We present the Spitzer Extragalactic Representative Volume Survey (SERVS), an 18 square degrees medium-deep survey at 3.6 and 4.5 microns with the post-cryogenic Spitzer Space Telescope to ~2 microJy (AB=23.1) depth of five highly observed astronomical fields (ELAIS-N1, ELAIS-S1, Lockman Hole, Chandra Deep Field South and XMM-LSS). SERVS is designed to enable the study of galaxy evolution as a function of environment from z~5 to the present day, and is the first extragalactic survey both large enough and deep enough to put rare objects such as luminous quasars and galaxy clusters at z>1 into their cosmological context. SERVS is designed to overlap with several key surveys at optical, near- through far-infrared, submillimeter and radio wavelengths to provide an unprecedented view of the formation and evolution of massive galaxies. In this paper, we discuss the SERVS survey design, the data processing flow from image reduction and mosaicing to catalogs, as well as coverage of ancillary data from other surveys in the SERVS fields. We also highlight a variety of early science results from the survey.
We explore the nature of heavily obscured quasar host galaxies at z~2 using deep Hubble Space Telescope WFC3/IR imaging of 28 Dust Obscured Galaxies (DOGs) to investigate the role of major mergers in driving black hole growth. The high levels of obscuration of the quasars selected for this study act as a natural coronagraph, blocking the quasar light and allowing a clear view of the underlying host galaxy. The sample of heavily obscured quasars represents a significant fraction of the cosmic mass accretion on supermassive black holes as the quasars have inferred bolometric luminosities around the break of the quasar luminosity function. We find that only a small fraction (4%, at most 11-25%) of the quasar host galaxies are major mergers. Fits to their surface brightness profiles indicate that 90% of the host galaxies are either disk dominated, or have a significant disk. This disk-like host morphology, and the corresponding weakness of bulges, is evidence against major mergers and suggests that secular processes are the predominant driver of massive black hole growth. Finally, we suggest that the co-incidence of mergers and AGN activity is luminosity dependent, with only the most luminous quasars being triggered mostly by major mergers.
It was recently shown that the power spectrum in redshift space can be written as a sum of cross-power spectra between number weighted velocity moments. We investigate the properties of these power spectra for simulated galaxies and dark matter halos and compare them to the dark matter power spectra, generalizing the concept of the bias. Because all of the quantities are number weighted this approach is well defined even for sparse systems such as massive halos, in contrasts to the previous approaches to RSD where velocity correlations have been explored. We find that the number density weighting leads to a strong scale dependence of the bias terms for momentum density auto-correlation and cross-correlation with density. This trend becomes more significant for the more biased halos and leads to an enhancement of RSD power relative to the linear theory. Fingers-of-god effects, which in this formalism come from the correlations of the higher order moments beyond the momentum density, lead to smoothing of the power spectrum and can reduce this enhancement of power, but are relatively small for halos with no small-scale velocity dispersion. In comparison, for a more realistic galaxy sample with satellites the velocity dispersion generated by satellite motions inside the halos leads to a larger power suppression on small scales, but this depends on the satellite fraction. We investigate several statistics such as the two-dimensional power spectrum, its multipole moments, its powers of mu^2, and configuration space statistics. Overall we find that the nonlinear effects in realistic galaxy samples such as luminous red galaxies affect the redshift space clustering on very large scales: for example, the quadrupole moment is affected by 10% for k<0.1h/mpc, which means that these effects need to be understood if we want to extract cosmological information from the redshift space distortions.
We present 2" - 10" imaging of eleven transitions from nine molecular species across the nuclear bar in Maffei 2. The data were obtained with the BIMA and OVRO interferometers. The ten detected transitions are compared with existing CO isotopologues, HCN, CS and millimeter continuum data. Dramatic spatial variations among the mapped species are observed across the nuclear bar. A principle component analysis is performed to characterize correlations between the transitions, star formation and molecular column density. The analysis reveals that HCN, HNC, HCO+ and 3 mm continuum are tightly correlated, indicating a direct connection to massive star formation. We find two main morphologically distinct chemical groups, CH3OH, SiO and HNCO comprising the grain chemistry molecules, versus HCN, HNC, HCO+ and C2H, molecules strong in the presence of star formation. The grain chemistry molecules, HNCO, CH3OH and SiO, trace hydrodynamical bar shocks. The near constancy of the HNCO/CH3OH, SiO/CH3OH and SiO/HNCO ratios argue that shock properties are uniform across the nucleus. HCN/HCO+, HCN/HNC, HCN/CS and HCN/CO ratios are explained primarily by variations in density. High HCO+/N2H+ ratios are correlated with the C2H line, suggesting that this ratio may be a powerful new dense photon-dominated region (PDR) probe in external galaxies. C2H reveals a molecular outflow along the minor axis. The morphology and kinematics of the outflow are consistent with an outflow age of 6-7 Myrs.
We present a detailed analysis of high resolution H I observations of the Magellanic spiral galaxies NGC 4618 and NGC 4625. While the H I disk of NGC 4625 is remarkably quiescent with a nearly uniform velocity dispersion and no evidence of H I holes, there is a dynamic interplay between star formation and the distribution of neutral hydrogen in NGC 4618. We calculate the critical density for widespread star formation in each galaxy and find that star formation proceeds even where the surface density of the atomic gas is well below the critical density necessary for global star formation. There are strong spatial correlations in NGC 4618 between UV emission, 1.4 GHz radio continuum emission, and peaks in the H I column density. Despite the apparent overlap of the outer disks of the two galaxies, we find that they are kinematically distinct, indicating that NGC 4618 and NGC 4625 are not interacting. The structure of NGC 4618 and, in particular, the nature of its outer ring, are highly suggestive of an interaction, but the timing and nature of such an interaction remain unclear.
If a component of cosmological dark matter is made up of massive particles - such as sterile neutrinos - that decay with cosmological lifetime to emit photons, the reionization history of the universe would be affected, and cosmic microwave background anisotropies can be used to constrain such a decaying particle model of dark matter. The optical depth depends rather sensitively on the decaying dark matter particle mass m_{dm}, lifetime tau_{dm}, and the mass fraction of cold dark matter f that they account for in this model. Assuming that there are no other sources of reionization and using the WMAP 7-year data, we find that 250 eV < m_{dm} < 1 MeV, whereas 2.23*10^3 yr < tau_{dm} < 1.23*10^18 yr. The best fit values for m_{dm} and tau_{dm}/f are 17.3 keV and 2.03*10^16 yr respectively.
We update our prior work on the case B collisional-recombination spectrum of He I to incorporate \textit{ab initio} photoionisation cross-sections. This large set of accurate, self-consistent cross-sections represents a significant improvement in He I emissivity calculations because it largely obviates the piecemeal nature that has marked all modern works. A second, more recent set of \textit{ab initio} cross-sections is also available, but we show that those are less consistent with bound-bound transition probabilities than our adopted set. We compare our new effective recombination coefficients with our prior work and our new emissivities with those by other researchers, and we conclude with brief remarks on the effects of the present work on the He I error budget. Our calculations cover temperatures $5000 \le T_e \le 25000$ K and densities $10^1 \le n_e \le 10^{14}$ cm$^{-3}$. Full results are available online.
A new paradigm for active galactic jet kinematics has emerged through detailed investigations of BL Lac objects using very long baseline radio interferometry. In this new scheme, most, if not all, jet components appear to remain stationary with respect to the core but show significant non-radial motions. This paper presents results from our kinematic investigation of the jets of a statistically complete sample of radio-loud flat-spectrum active galaxies, focusing on the comparison between the jet kinematic properties of BL Lacs and flat-spectrum radio-quasars. It is shown that there is a statistically significant difference between the kinematics of the two AGN classes, with BL Lacs showing more bent jets, that are wider and show slower movement along the jet axis, compared to flat-spectrum radio-quasars. This is interpreted as evidence for helically structured jets.
Primordial Black Holes (PBH's) can form in the early Universe from the collapse of large density fluctuations. Tight observational limits on their abundance constrain the amplitude of the primordial fluctuations on very small scales which can not otherwise be constrained, with PBH's only forming from the extremely rare large fluctuations. The number of PBH's formed is therefore sensitive to small changes in the shape of the tail of the fluctuation distribution, which itself depends on the amount of non-Gaussianity present. We study, for the first time, how quadratic and cubic local non-Gaussianity of arbitrary size (parameterised by f_nl and g_nl respectively) affects the PBH abundance and the resulting constraints on the amplitude of the fluctuations on very small scales. Intriguingly we find that even non-linearity parameters of order unity have a significant impact on the PBH abundance. The sign of the non-Gaussianity is particularly important, with the constraint on the allowed fluctuation amplitude tightening by an order of magnitude as f_nl changes from just -0.5 to 0.5. We find that if PBH's are observed in the future, then regardless of the amplitude of the fluctuations, non-negligible negative f_nl would be ruled out. Finally we show that g_nl can have an even larger effect on the number of PBH's formed than f_nl.
A bouncing cosmology with an initial matter-dominated phase of contraction during which scales which are currently probed with cosmological observations exit the Hubble radius provides a mechanism alternative to inflation for producing a nearly scale-invariant spectrum of cosmological perturbations. In this review article I first discuss the evolution of cosmological fluctuations in the matter bounce scenario, and then discuss various attempts at realizing such a scenario. Observational signatures which will allow the matter bounce to be distinguished from the inflationary paradigm are also discussed.
In this paper we describe the first data release of the the Visible and
Infrared Survey Telescope for Astronomy (VISTA) Deep Extragalactic Observations
(VIDEO) survey. VIDEO is a ~12degree^2 survey in the near-infrared Z,Y,J,H and
K_s bands, specifically designed to enable the evolution of galaxies and large
structures to be traced as a function of both epoch and environment from the
present day out to z=4, and active galactic nuclei (AGN) and the most massive
galaxies up to and into the epoch of reionization. With its depth and area,
VIDEO will be able to fully explore the period in the Universe where AGN and
starburst activity were at their peak and the first galaxy clusters were
beginning to virialize. VIDEO therefore offers a unique data set with which to
investigate the interplay between AGN, starbursts and environment, and the role
of feedback at a time when it was potentially most crucial.
We provide data over the VIDEO-XMM3 tile, which also covers the
Canada-France-Hawaii-Telescope Legacy Survey Deep-1 field (CFHTLS-D1). The
released VIDEO data reach a 5-sigma AB-magnitude depth of Z=25.7, Y=24.5,
J=24.4, H=24.1 and K_s=23.8 in 2 arcsec diameter apertures (the full depth of
Y=24.6 will be reached within the full integration time in future releases).
The data are compared to previous surveys over this field and we find good
astrometric agreement with the Two-Micron All Sky Survey, and source counts in
agreement with the recently released UltraVISTA survey data. The addition of
the VIDEO data to the CFHTLS-D1 optical data increases the accuracy of
photometric redshifts and significantly reduces the fraction of catastrophic
outliers over the redshift range 0<z<1 from 5.8 to 3.1 per cent in the absence
of an i-band luminosity prior. (Truncated Abstract)
In this letter, we study the effects of an interaction between dark matter and dark energy through a two scalar field model with a potential $V(\phi,\chi)=e^{-\lambda\phi}P(\phi,\chi)$, where $P(\phi,\chi)$ is a polynomial. We show that features of the present Universe are reproduced for a large range of the bare mass of the dark matter field. Simple modifications of the potential are studied, revealing important implications of the interaction, including the possibility of transient acceleration solutions.
The review contains an analysis of the observed and model curves of the interstellar extinction and polarization. The observations mainly give information on dust in diffuse and translucent interstellar clouds. The features of various dust grain models including spherical/non-spherical, homogeneous/inhomogeneous particles are discussed. A special attention is devoted to the analysis of the grain size distributions, alignment mechanisms and magnetic field structure in interstellar clouds. It is concluded that the interpretation of interstellar extinction and polarization is not yet complete.
We show how the redshift and peak-flux distributions of gamma-ray bursts (GRBs) have an observation time dependence that can be used to discriminate between different burst populations. We demonstrate how observation time relations can be derived from the standard integral distributions and that they can differentiate between GRB populations detected by both the BATSE and \emph{Swift} satellites. Using \emph{Swift} data we show that a redshift--observation-time relation (log\,$Z$\,--\,log\,$T$) is consistent with both a peak-flux\,--\,observation time relation (log\,$P$\,--\,log\,$T$) and a standard log\,$N$\,--\,log\,$P$ brightness distribution. As the method depends only on rarer small-$z$ events, it is invariant to high-$z$ selection effects. We use the log\,$Z$\,--\,log\,$T$ relation to show that sub-luminous GRBs are a distinct population occurring at a higher rate of order $150^{+180}_{-90} \mathrm{Gpc}^{-3}\mathrm{yr}^{-1}$. Our analysis suggests that GRB 060505 -- a relatively nearby GRB observed without any associated supernova -- is consistent with a sub-luminous population of bursts. Finally, we suggest that our relations can be used as a consistency test for some of the proposed GRB spectral energy correlations.
Microphysics of weakly magnetized relativistic collisionless shock waves, corroborated by recent high performance numerical simulations, indicate the presence of a microturbulent layer of large magnetic field strength behind the shock front, which must decay beyond some hundreds of skin depths. The present paper discusses the dynamics of such microturbulence, borrowing from these same numerical simulations, and calculates the synchrotron signature of a powerlaw of shock accelerated particles. The decaying microturbulent layer is found to leave distinct signatures in the spectro-temporal evolution of the spectrum $F_\nu \propto t^{-\alpha}\nu^{-\beta}$ of a decelerating blast wave, which are potentially visible in early multi-wavelength follow-up observations of gamma-ray bursts. This paper also discusses the influence of the evolving microturbulence on the acceleration process, with particular emphasis on the maximal energy of synchrotron afterglow photons, which falls in the GeV range for standard gamma-ray burst parameters. Finally, this paper argues that the evolving microturbulence plays a key role in shaping the spectra of recently observed gamma-ray bursts with extended GeV emission, such as GRB090510.
Links to: arXiv, form interface, find, astro-ph, recent, 1206, contact, help (Access key information)
We present the first detailed study of the stellar populations of star-forming galaxies at z~1.5, which are selected by their [O II] emission line, detected in narrow-band surveys. We identified ~1,300 [O II] emitters at z=1.47 and z=1.62 in the Subaru Deep Field with rest-frame EWs above 13\AA. Optical and near-infrared spectroscopic observations for ~10% of our samples show that our two-color identification of [O II] emission-line galaxies is 99% successful. We analyze the multi-wavelength properties of a subset of ~1,200 galaxies with the best photometry. They have average rest-frame EW of 45\AA, stellar mass of 3 x 10^9 M_sun, and stellar age of 100 Myr. In addition, our SED fitting and broad-band colors indicate that [O II] emitters span the full range of galaxy populations at z~1.5. We also find that 80% of [O II] emitters are also photometrically classified as "BX/BM" (UV) galaxies and/or the star-forming "BzK" (near-IR) galaxies. Our [O II] emission line survey produces a far more complete, and somewhat deeper sample of z~1.5 galaxies than either the BX/BM or sBzK selection alone. We constructed average SEDs and find that higher [O II] EW galaxies have somewhat bluer continua. SED model-fitting shows that they have on average half the stellar mass of galaxies with lower [O II] EW. The observed [O II] luminosity is well-correlated with the far-UV continuum with a slope slightly less than one (0.89). However, this offset is only marginally significant (< 1\sigma). The fit also suggests that [O II] can be used as a SFR indicator, but with an additional systematic uncertainty of ~0.2 dex.
We study the shapes of galaxy dark matter haloes by measuring the anisotropy of the weak gravitational lensing signal around galaxies in the second Red-sequence Cluster Survey (RCS2). We determine the average shear anisotropy within the virial radius for three lens samples: all galaxies with 19<m_r'<21.5, and the `red' and `blue' samples, whose lensing signals are dominated by massive low-redshift early-type and late-type galaxies, respectively. To study the environmental dependence of the lensing signal, we separate each lens sample into an isolated and clustered part and analyse them separately. We also measure the azimuthal dependence of the distribution of physically associated galaxies around the lens samples. We find that these satellites preferentially reside near the major axis of the lenses, and constrain the angle between the major axis of the lens and the average location of the satellites to <theta>=43.7 deg +/- 0.3 deg for the `all' lenses, <theta>=41.7 deg +/- 0.5 deg for the `red' lenses and <theta>=42.0 deg +/- 1.4 deg for the `blue' lenses. For the `all' sample, we find that the anisotropy of the galaxy-mass cross-correlation function <f-f_45>=0.23 +/- 0.12, providing weak support for the view that the average galaxy is embedded in, and preferentially aligned with, a triaxial dark matter halo. Assuming an elliptical Navarro-Frenk-White (NFW) profile, we find that the ratio of the dark matter halo ellipticity and the galaxy ellipticity f_h=e_h/e_g=1.50+1.03-1.01, which for a mean lens ellipticity of 0.25 corresponds to a projected halo ellipticity of e_h=0.38+0.26-0.25 if the halo and the lens are perfectly aligned. For isolated galaxies of the `all' sample, the average shear anisotropy increases to <f-f_45>=0.51+0.26-0.25 and f_h=4.73+2.17-2.05, whilst for clustered galaxies the signal is consistent with zero. (abridged)
Advancements in infrared IR open up the possibility to spatially resolve AGN on the parsec-scale level and study the circumnuclear dust distribution, commonly referred to as the "dust torus", that is held responsible for the type 1/type 2 dichotomy of AGN. We used the mid-IR beam combiner MIDI together with the 8m telescopes at the VLTI to observe the nucleus of the Seyfert 2 galaxy NGC 424, achieving an almost complete coverage of the uv-plane accessible by the available telescope configurations. We detect extended mid-IR emission with a relatively baseline- and model-independent mid-IR half-light radius of (2.0 \pm 0.2) pc \times (1.5 \pm 0.3) pc (averaged over the 8-13 {\mu}m wavelength range). The extended mid-IR source shows an increasing size with wavelength. The orientation of the major axis in position angle -27deg is closely aligned with the system axis as set by optical polarization observations. Torus models typically favor extension along the mid-plane at mid-IR wavelengths instead. Therefore, we conclude that the majority of the pc-scale mid-IR emission (>~60%) in this type 2 AGN originates from optically-thin dust in the polar region of the AGN, a scenario consistent with the near- to far-IR SED. We suggest that a radiatively-driven dusty wind, possibly launched in a puffed-up region of the inner hot part of the torus, is responsible for the polar dust. In this picture, the torus dominates the near-IR emission up to about 5 {\mu}m, while the polar dust is the main contributor to the mid-IR flux. Our results of NGC 424 are consistent with recent observations of the AGN in the Circinus galaxy and resemble large-scale characteristics of other objects. If our results reflect a general property of the AGN population, the current paradigm for interpreting and modeling the IR emission of AGN have to be revised. (abridged)
Recent work has suggested that the stellar initial mass function (IMF) is not universal, but rather is correlated with galaxy stellar mass, stellar velocity dispersion, or morphological type. In this paper, we investigate variations of the IMF within individual galaxies. For this purpose, we use strong lensing and gas kinematics to measure independently the normalization of the IMF of the bulge and disk components of a sample of 5 massive spiral galaxies with substantial bulge components taken from the SWELLS survey. We find that the stellar mass of the bulges is tightly constrained by the lensing and kinematic data and consistent with that obtained by stellar population synthesis models fits to their colours only by assuming a Salpeter-like normalisation of the IMF. Conversely, the disk masses are less well constrained due to degeneracies with the dark matter halo, but are consistent with Milky Way type IMFs in agreement with previous studies. The disks are submaximal at 2.2 disk scale lengths, but due to the contribution of the bulges, the galaxies are baryon dominated at 2.2 disk scale lengths. Globally, our inferred IMF normalisation is consistent with that found for early-type galaxies of comparable stellar mass (>10^11 M_sun). Our results provide evidence for a non-universal IMF within the different components of spiral galaxies, adding to the well-known differences in stellar populations between disks and bulges.
To investigate possible variations in the stellar initial mass function (IMF) in red-sequence galaxies, we have obtained infrared spectroscopy with Subaru/FMOS for a sample of 92 red-sequence galaxies in the Coma cluster. Velocity dispersions, ages and element abundances for these galaxies have been previously determined from optical data. By stacking the FMOS spectra in the rest frame, removing sky-subtraction residuals and other artefacts fixed in the observed frame, we derive composite spectra in the 9600-10500 Angstrom range for galaxies grouped according to their velocity dispersion or Mg/Fe ratio. We measure the Wing-Ford band of FeH and a new index centred on a CaI line at 10345 Angstrom; these features are strong in cool dwarf stars, and hence reflect the form of the IMF at low mass (<0.5M_sun) The CaI line, unlike the Wing-Ford band and other `classical' IMF indicators (NaI doublet, CaII triplet), is unaffected by the abundance of sodium. We compare the measured indices against predictions from spectral synthesis models matched to the element abundances estimated from the optical data. Binning galaxies by velocity dispersion, we find that both the Wing-Ford and CaI index measurements are best reproduced by models with the Salpeter IMF. There is no clear evidence for an increase in dwarf-star content with velocity dispersion. Binning the observed galaxies instead by Mg/Fe ratio, the behaviour of both indices implies a trend of IMF from Chabrier-like, at abundance ratios close to solar, to Salpeter or heavier for highly alpha-enhanced populations. At face value, this suggests that the IMF depends on the mode of star formation, with intense rapid star-bursts generating a larger population of low-mass stars.
We study the matter and velocity divergence power spectra in a f(R) gravity theory and their time evolution measured from several large-volume N-body simulations with varying box sizes and resolution. We find that accurate prediction of the matter power spectrum in f(R) gravity places stronger requirements on the simulation than is the case with LCDM, because of the nonlinear nature of the fifth force. Linear perturbation theory is shown to be a poor approximation for the f(R) models, except when the chameleon effect is very weak. We show that the relative differences from the fiducial LCDM model are much more pronounced in the nonlinear tail of the velocity divergence power spectrum than in the matter power spectrum, which suggests that future surveys which target the collection of peculiar velocity data will open new opportunities to constrain modified gravity theories. A close investigation of the time evolution of the power spectra shows that there is a pattern in the evolution history, which can be explained by the properties of the chameleon-type fifth force in f(R) gravity. Varying the model parameter |f_R0|, which quantifies the strength of the departure from standard gravity, mainly varies the epoch marking the onset of the fifth force, as a result of which the different f(R) models are in different stages of the same evolutionary path at any given time
We have used deep, HST, near-IR imaging to study the morphological properties of the most massive galaxies at high z, modelling the WFC3/IR H-band images of the ~200 galaxies in the CANDELS-UDS field with 1 < z_phot < 3, and stellar masses M_star > 10^11 M_sun. We have used both single-Sersic and bulge+disk models, have investigated the errors/biases introduced by uncertainties in the background and the PSF, and have obtained formally-acceptable model fits to >90% of the galaxies. Our results indicate that these massive galaxies at 1 < z < 3 lie both on and below the local size-mass relation, with a median R_e~2.6 kpc, a factor of ~2.3 smaller than comparably-massive local galaxies. Moreover, we find that bulge-dominated objects in particular show evidence for a growing bimodality in the size-mass relation with increasing z, and by z > 2 the compact bulges display effective radii a factor ~4 smaller than local ellipticals of comparable mass. These trends appear to extend to the bulge components of disk-dominated galaxies, and vice versa. We also find that, while such massive galaxies at low z are bulge-dominated, at 1 < z < 2 they are predominantly mixed bulge+disk systems, and by z > 2 they are mostly disk-dominated. The majority of the disk-dominated galaxies are actively forming stars, but this is also true for many of the bulge-dominated systems. Interestingly, however, while most of the quiescent galaxies are bulge-dominated, we find that a significant fraction (25-40%) of the most quiescent galaxies have disk-dominated morphologies. Thus, while our results show that the massive galaxy population is undergoing dramatic changes at this crucial epoch, they also suggest that the physical mechanisms which quench star-formation activity are not simply connected to those responsible for the morphological transformation of massive galaxies into present-day giant ellipticals.
Observations with Subaru telescope have detected surprisingly strong Lyman continuum (LyC; $\sim900$ \AA\ in the rest-frame) from some Lyman $\alpha$ emitters (LAEs) at $z=3.1$. We have examined the stellar population which simultaneously accounts for the strength of the LyC and the spectral slope of non-ionizing ultraviolet of the LAEs. As a result, we have found that stellar populations with metallicity $Z\geq1/50 Z_\odot$ can explain the observed LyC strength only with a very top-heavy initial mass function (IMF; $< m > \sim 50 M_\odot$). However, the critical metallicity for such an IMF is expected to be much lower. A very young ($\sim1$ Myr) and massive ($\sim100$ $M_\odot$) extremely metal-poor ($Z\leq5\times10^{-4}Z_\odot$) or metal-free (so-called Population III) stellar population can also reproduce the observed LyC strength if the mass fraction of such 'primordial' stellar population is $\sim1$% in total stellar mass of the LAEs.
Models of spontaneous wave function collapse modify the linear Schr\"{o}dinger equation of standard Quantum Mechanics by adding stochastic non-linear terms to it. The aim of such models is to describe the quantum (linear) nature of microsystems along with the classical nature (violation of superposition principle) of macroscopic ones. The addition of such non-linear terms in the Schr\"{o}dinger equation leads to non-conservation of energy of the system under consideration. Thus, a striking feature of collapse models is to heat non-relativistic particles with a constant rate. If such a process is physical, then it has the ability to perturb the well-understood thermal history of the universe. In this article we will try to investigate the impacts of such heating terms on standard evolution of non-relativistic matter and on the formation of CMBR. We will use the CSL model, the most widely used collapse model. We will also put constraints on the CSL collapse rate $\lambda$ by considering that the standard evolution of non-relativistic matter is not hampered and the observed precise blackbody spectrum of CMBR would not get distorted (in the form of $\mu-$type and $y-$type distortions) so as to violate the observed bounds.
I outline the prospects for performing weak lensing studies with the new generation of radio telescopes that are coming online now and in the future. I include a description of a proposed technique to use polarization observations in radio weak lensing analyses which could prove extremely useful for removing a contaminating signal from intrinsic alignments. Ultimately, the Square Kilometre Array promises to be an exceptional instrument for performing weak lensing studies due to the high resolution, large area surveys which it will perform. In the nearer term, the e-MERLIN instrument in the UK offers the high sensitivity and sub-arcsec resolution required to prove weak lensing techniques in the radio band. I describe the SuperCLASS survey -- a recently accepted e-MERLIN legacy programme which will perform a pioneering radio weak lensing analysis of a supercluster of galaxies.
Spectral distortion of the cosmic microwave background provides a unique opportunity to probe primordial perturbations on very small scales by performing large-scale measurements. We discuss in a systematic and pedagogic way all the relevant physical phenomena involved in the production and evolution of the mu-type spectral distortion. Our main results agree with previous estimates (in particular we show that a recently found factor of 3/4 arises from relativistic corrections to the wave energy). We also discuss several subleading corrections such as adiabatic cooling and the effects of bulk viscosity, baryon loading and photon heat conduction. Finally we calculate the transfer function for mu-distortions between the end of the mu-era and now.
We present results of broad band photometric reverberation mapping (RM) to measure the radius of the broad line region, and subsequently the black hole mass (M$_{\rm BH}$), in the nearby, low luminosity active galactic nuclei (AGN) NGC 4395. Using the Wise Observatory's 1m telescope equipped with the SDSS g$'$, r$'$ and i$'$ broad band filters, we monitored NGC 4395 for 9 consecutive nights and obtained 3 light curves each with over 250 data points. The g$'$ and r$'$ bands include time variable contributions from H$\beta$ and H$\alpha$ (respectively) plus continuum. The i$'$ band is free of broad lines and covers exclusively continuum. We show that by looking for a peak in the difference between the cross-correlation and the auto-correlation functions for all combinations of filters, we can get a reliable estimate of the time lag necessary to compute M$_{\rm BH}$. We measure the time lag for H$\alpha$ to be $3.6 \pm 0.8 $ hours, comparable to previous studies using the line resolved spectroscopic RM method. We argue that this lag implies a black hole mass of M$_{\rm BH} = (4.9 \pm 2.6) \times 10^{4}$ \Msun .
We present APEX SABOCA 350micron and LABOCA 870micron observations of 11 representative examples of the rare, extremely bright (S_1.4mm > 15mJy), dust-dominated millimeter-selected galaxies recently discovered by the South Pole Telescope (SPT). All 11 sources are robustly detected with LABOCA with 40 < S_870micron < 130mJy, approximately an order of magnitude higher than the canonical submillimeter galaxy (SMG) population. Six of the sources are also detected by SABOCA at >3sigma, with the detections or upper limits providing a key constraint on the shape of the spectral energy distribution (SED) near its peak. We model the SEDs of these galaxies using a simple modified blackbody and perform the same analysis on samples of SMGs of known redshift from the literature. These calibration samples inform the distribution of dust temperature for similar SMG populations, and this dust temperature prior allows us to derive photometric redshift estimates and far infrared luminosities for the sources. We find a median redshift of <z> = 3.0, higher than the <z> = 2.2 inferred for the normal SMG population. We also derive the apparent size of the sources from the temperature and apparent luminosity, finding them to appear larger than our unlensed calibration sample, which supports the idea that these sources are gravitationally magnified by massive structures along the line of sight.
Infrared 3.6 to 8 micron images of the Extended Groth Strip yield plausible counterpart identifications for all but one of 510 radio sources in the AEGIS20 S(1.4 GHz) > 50 micro-Jy sample. This is the first such deep sample that has been effectively 100% identified. Achieving the same identification rate at R-band would require observations reaching R_AB > 27. Spectroscopic redshifts are available for 46% of the sample and photometric redshifts for an additional 47%. Almost all of the sources with 3.6 micron AB magnitudes brighter than 19 have spectroscopic redshifts z < 1.1, while fainter objects predominantly have photometric redshifts with 1 \lapprox z \lapprox 3. Unlike more powerful radio sources that are hosted by galaxies having large stellar masses within a relatively narrow range, the AEGIS20 counterparts have stellar masses spanning more than a factor of 10 at z \sim 1. The sources are roughly 10--15% starbursts at z \lapprox 0.5 and 20--25% AGNs mostly at z > 1 with the remainder of uncertain nature.
Steady accretion of a radiating gas onto a central mass point is described and compared to classic Bondi accretion. Radiation losses are essential for accretion flows to be observed. Unlike Bondi flows, radiating Bondi flows pass through a sonic point at a finite radius and become supersonic near the center. The morphology of all radiating Bondi flows is described by a single dimensionless parameter. In radiating Bondi flows the mass accretion rate varies approximately as the first power of the central mass -- this differs significantly from the quadratic dependence on the central mass in classical Bondi flows. Mass accretion rates onto galaxy or cluster-centered black holes estimated from traditional and radiating Bondi flows are significantly different. In radiating Bondi flows the gas temperature increases at large radii, as in the cores of many galaxy groups and clusters, allowing radiating Bondi flows to merge naturally with gas arriving from their cluster environments. Some radiating flows cool completely before reaching the center of the flow, and this also occurs in cooling site flows in which there is no central gravitating mass.
We calculate the baryon asymmetry produced at the electroweak phase transition by quasi-degenerate third generation sfermions in the minimal supersymmetric extension of the Standard Model. We evaluate constraints from Higgs searches, from collider searches for supersymmetric particles, and from null searches for the permanent electric dipole moment (EDM) of the electron, of the neutron and of atoms. We find that resonant sfermion sources can in principle provide a large enough baryon asymmetry in various corners of the sfermion parameter space, and we focus, in particular, on the case of large $\tan\beta$, where third-generation down-type (s)fermions become relevant. We show that in the case of stop and sbottom sources, the viable parameter space is ruled out by constraints from the non-observation of the Mercury EDM. We introduce a new class of CP violating sources, quasi-degenerate staus, that escapes current EDM constraints while providing large enough net chiral currents to achieve successful "slepton-mediated" electroweak baryogenesis.
Ground-based optical surveys such as PanSTARRS, DES, and LSST, will produce large catalogs to limiting magnitudes of r > 24. Star-galaxy separation will pose a major challenge to such surveys because galaxies---even very compact galaxies---outnumber halo stars at these depths. Here we investigate photometric classification techniques on stars and galaxies with intrinsic FWHM < 0.2 arcsec. We consider unsupervised SED template fitting and supervised, data-driven Support Vector Machines (SVM). For template fitting, we use a Maximum Likelihood (ML) method and a new Hierarchical Bayesian (HB) method, in which we learn the prior distribution of template probabilities by optimizing the likelihood for the entire dataset. SVM requires training data to classify unknown sources; ML and HB don't. We consider both i.) a best-case scenario (SVM_best) in which the training data is (unrealistically) a random sampling of the data in both signal-to-noise and demographics, and ii.) a more realistic scenario in which the SVM is trained on higher signal-to-noise data (SVM_real) at brighter apparent magnitudes. Testing with COSMOS ugriz data we find that HB outperforms ML, delivering ~80% completeness in both star and galaxy samples, with purity of ~40-90% and ~70-90% for stars and galaxies, respectively. We find no algorithm delivers perfect performance, and that studies of M-giant and metal-poor main-sequence turnoff stars may be most affected by poor star-galaxy separation. We measure the area under the ROC curve to assess the relative performance of the approaches and find a best-to-worst ranking of SVM_best, HB, ML, and SVM_real. We conclude, therefore, that a well trained SVM will outperform template-fitting methods. However, a normally trained SVM performs worse. Thus, Hierarchical Bayesian template fitting may prove to be the optimal method for source classification in future surveys.
We study the spectrum of cosmological fluctuations in scenarios such as Galilean Genesis in which a spectator scalar field acquires a scale-invariant spectrum of perturbations during an early phase which asymptotes in the far past to Minkowski space-time. In the case of minimal coupling to gravity and standard scalar field Lagrangian, the induced curvature fluctuations depend quadratically on the spectator field and are hence non-scale-invariant and highly non-Gaussian. We show that if higher dimensional operators (the same operators that lead to the {\eta}-problem for inflation) are considered, a linear coupling between background and spectator field fluctuations is induced which leads to scale-invariant and Gaussian curvature fluctuations.
We present one-dimensional models of the hot gas in dark-matter halos, which both predict the existence of cool cores and explain their structure. Our models are directly applicable to semi-analytic models (SAMs) of galaxy formation. We have previously argued that filaments of cold (~10^4 K) gas condense out of the intracluster medium (ICM) in hydrostatic and thermal equilibrium when the ratio of the thermal instability timescale to the free-fall time $t_{TI}/t_{ff}$ falls below 5-10. This criterion corresponds to an upper limit on the density of the ICM and motivates a model in which a density core forms wherever $t_{TI}/t_{ff} \lesssim 10$. Consistent with observations and numerical simulations, this model predicts larger and more tenuous cores for lower-mass halos---while the core density in a cluster may be as large as ~ 0.1 cm^{-3}, the core density in the Galactic halo should not exceed ~ 10^{-4} cm^{-3}. Our models produce a favorable match to the observational X-ray luminosity-temperature (Lx-Tx) relation. For halo masses $\lesssim 10^{13}$ Msun the core size approaches the virial radius. Thus, most of the baryons in such halos cannot be in the hot ICM, but either in the form of stars or in the form of hot gas beyond the virial radius. Because of the smaller mass in the ICM and much larger mass available for star formation, the majority of the baryons in low mass halos ($\lesssim 10^{13}$ Msun) can be expelled beyond the virial radius due to supernova feedback. This can account for the baryons `missing' from low mass halos, such as the Galactic halo.
It is well known that current spectroscopic determinations of the chemical composition of the Sun are starkly at odds with the metallicity implied by helioseismology. We propose that the discrepancy may be due to conversion of photons to a new light boson in the solar photosphere. We investigate the impact of particles with axion-like interactions with the photon on the inferred photospheric abundances. Conversion of photons into new light bosons can in principle easily produce the +0.2 dex change in derived abundances required to reconcile spectroscopic and helioseismological determinations of the solar metallicity. We show that this is however not possible for any of the presently-allowed parameter space of either the QCD axion or a standard axion-like particle. We speculate that other models involving photon-boson mixing, such as hidden photons, might prove more successful.
In previous works, it was shown that the Lagrangians and Hamiltonians of cosmological linear scalar, vector and tensor perturbations of homogeneous and isotropic space-times with flat spatial sections containing a perfect fluid can be put in a simple form through the implementation of canonical transformations and redefinitions of the lapse function, without ever using the background classical equations of motion. In this paper, we generalize this result to general fluids, which includes entropy perturbations, and to arbitrary spacelike hyper-surfaces through a new method together with the Faddeev-Jackiw procedure for the constraint reduction. A simple second order Hamiltonian involving the Mukhanov-Sasaki variable is obtained, again without ever using the background equations of motion.
Despite expanding research activity in gravitational lens modeling, there is no particular software which is considered a standard. Much of the gravitational lens modeling software is written by individual investigators for their own use. Some gravitational lens modeling software is freely available for download but is widely variable with regard to ease of use and quality of documentation. This review of 12 software packages was undertaken to provide a single source of information. Gravitational lens models are classified as parametric models or non-parametric models, and can be further divided into research and educational software. Software used in research includes GravLens / LensModel, Lenstool, Lensperfect, Glafic, PixeLens, SimpLens, Lensview, and GRALE. In this review, GravLensHD, G-Lens, Gravitational Lensing and Lens are categorized as educational programs that are useful for demonstrating various aspects of lensing. Each of the 12 software packages is reviewed with regard to software features (installation, documentation, files provided, etc.) and lensing features (type of model, input data, output data, etc.) as well as a brief review of studies where they have been used. Recent studies have demonstrated the utility of strong gravitational lensing data for mass mapping, and suggest increased use of these techniques in the future. Coupled with the advent of greatly improved imaging, new approaches to modeling of strong gravitational lens systems are needed. This is the first systematic review of strong gravitational lens modeling software, providing investigators with a starting point for future software development to further advance gravitational lens modeling research.
In 2008 AGILE and Fermi detected gamma-ray flaring activity from the unidentified EGRET source 3EG J1236+0457, recently associated with a flat spectrum radio quasar GB6 J1239+0443 at z=1.762. The optical counterpart of the gamma-ray source underwent a flux enhancement of a factor 15-30 in 6 years, and of ~10 in six months. We interpret this flare-up in terms of a transition from an accretion-disk dominated emission to a synchrotron-jet dominated one. We analysed a Sloan Digital Sky Survey (SDSS) archival optical spectrum taken during a period of low radio and optical activity of the source. We estimated the mass of the central black hole using the width of the CIV emission line. In our work, we have also investigated SDSS archival optical photometric data and UV GALEX observations to estimate the thermal-disk emission contribution of GB6 J1239+0443. Our analysis of the gamma-ray data taken during the flaring episodes indicates a flat gamma-ray spectrum, with an extension of up to 15 GeV, with no statistically-relevant sign of absorption from the broad line region, suggesting that the blazar-zone is located beyond the broad line region. This result is confirmed by the modeling of the broad-band spectral energy distribution (well constrained by the available multiwavelength data) of the flaring activity periods and by the accretion disk luminosity and black hole mass estimated by us using archival data.
We propose two detection techniques that take advantage of a small sky area approximation and are based on modifications of the "internal linear combination" (ILC) method, an approach widely used in Cosmology for the separation of the various components that contribute to the microwave background. The main advantage of the proposed approach, especially in handling multi-frequency maps of the same region, is that it does not require the "a priori" knowledge of the spatial power-spectrum of either the CMB and/or the Galactic foreground. Hence, it is more robust, easier and more intuitive to use. The performance of the proposed algorithms is tested with numerical experiments that mimic the physical scenario expected for high Galactic latitude observations with the Atacama Large Millimeter/submillimeter Array (ALMA).
Links to: arXiv, form interface, find, astro-ph, recent, 1206, contact, help (Access key information)
We present IRAM Plateau de Bure Interferometer observations of the 12CO(3-2) emission from two far-infrared luminous QSOs at z ~ 2.5 selected from the Herschel-ATLAS survey. These far-infrared bright QSOs were selected to have supermassive black holes (SMBHs) with masses similar to those thought to reside in sub-millimetre galaxies (SMGs) at z ~ 2.5; making them ideal candidates as systems in transition from an ultraluminous infrared galaxy phase to a sub-mm faint, unobscured, QSO. We detect 12CO(3-2) emission from both QSOs and we compare their baryonic, dynamical and SMBH masses to those of SMGs at the same epoch. We find that these far-infrared bright QSOs have similar dynamical but lower gas masses than SMGs. In particular we find that far-infrared bright QSOs have ~50+-23% less warm/dense gas than SMGs, which combined with previous results showing the QSOs lack the extended, cool reservoir of gas seen in SMGs, suggests that they are at a different evolutionary stage. This is consistent with the hypothesis that far-infrared bright QSOs represent a short (~1Myr) but ubiquitous phase in the transformation of dust obscured, gas-rich, starburst-dominated SMGs into unobscured, gas-poor, QSOs.
We predict the space density of molecular gas reservoirs in the Universe, and place a lower limit on the number counts of carbon monoxide (CO), hydrogen cyanide (HCN) molecular and [CII] atomic emission lines in blind redshift surveys in the submillimeter-centimeter spectral regime. Our model uses: (a) recently available HCN Spectral Line Energy Distributions (SLEDs) of local Luminous Infrared Galaxies (LIRGs, L_IR>10^11 L_sun), (b) a value for epsilon=SFR/M_dense(H_2) provided by new developments in the study of star formation feedback on the interstellar medium and (c) a model for the evolution of the infrared luminosity density. Minimal 'emergent' CO SLEDs from the dense gas reservoirs expected in all star-forming systems in the Universe are then computed from the HCN SLEDs since warm, HCN-bright gas will necessarily be CO-bright, with the dense star-forming gas phase setting an obvious minimum to the total molecular gas mass of any star-forming galaxy. We include [CII] as the most important of the far-infrared cooling lines. Optimal blind surveys with the Atacama Large Millimeter Array (ALMA) could potentially detect very distant (z~10-12) [CII] emitters in the >ULIRG galaxy class at a rate of ~0.1-1 per hour (although this prediction is strongly dependent on the star formation and enrichment history at this early epoch), whereas the (high-frequency) Square Kilometer Array (SKA) will be capable of blindly detecting z>3 low-J CO emitters at a rate of ~40-70 per hour. The [CII] line holds special promise for the detection of metal-poor systems with extensive reservoirs of CO-dark molecular gas where detection rates with ALMA can reach up to 2-7 per hour in Bands 4-6.
We make use of our 'minimal' cold interstellar medium (ISM) emission line model that predicts the molecular and atomic line emission per unit dense, star-forming gas mass (Geach & Papadopoulos 2012; Paper I) to examine the utility of key line ratios in surveys of the so-called star formation 'mode' as traced by xi_SF = M_dense(H_2)/M_total(H_2). We argue that xi_SF and its proxies provide very sensitive, extinction-free discriminators of rapid starburst/merger-driven versus secular quiescent/disk-like stellar mass assembly, with the most promising diagnostic to be applied in the near-future being CO(4-3)/[CI](1-0). These lines are accessible across nearly the full range 0<z<2 (thus covering the bulk of galaxy evolution) with the Atacama Large Millimeter Array. In addition to their diagnostic power, another advantage of this combination is the similar observed frequencies (Delta nu_0 ~ 30 GHz) of the lines, resulting in nearly spatially-matched beams for a fixed aperture, thus mitigating the effects of resolution/morphology bias in the interpretation of galaxy-averaged line ratios. Finally we discuss the capability of deep blind redshift surveys with the high frequency component of the Square Kilometer Arrray (SKA) in discovering H_2-rich galaxies with very low xi_SF values. These could be the progenitors of starburst galaxies seen prior to the onset of star formation; such galaxies could be a class of extreme outliers from local (gas surface density)-(star formation rate) scaling laws, which would exclude them from current star formatation or stellar mass selected samples. Our conservative model suggests that SKA could detect such systems residing at z~3 at a rate of 20-200 per hour.
A significant fraction of the total photospheric light in nearby galaxy clusters is thought to be contained within the diffuse intracluster light (ICL), which extends 100s of kpc from cluster cores. The study of the ICL can reveal details of the evolutionary histories and processes occurring within galaxy clusters, however since it has a very low surface brightness it is often difficult to detect. We present here the first measurements of the ICL as a fraction of total cluster light at z \sim 1 using deep J-band (1.2 {\mu}m) imaging from HAWK-I on the VLT. We investigate the ICL in 6 X-ray selected galaxy clusters at 0.8< z <1.2 and find that the ICL below isophotes {\mu}(J) = 22 mag/arcsec2 constitutes 1-4% of the total cluster light within a radius R500. This is broadly consistent with simulations of the ICL at a similar redshift and when compared to nearby observations suggests that the fraction of the total cluster light that is in the ICL has increased by a factor 2 - 4 since z\sim1. We also find the fraction of the total cluster light contained within the Brightest Cluster Galaxy (BCG) to be 2.0-6.3% at these redshifts, which in 5 out of 6 cases is larger than the fraction of the ICL component, in contrast to results from nearby clusters. This suggests that the evolution in cluster cores involves substantial stripping activity at late times, in addition to the early build up of the BCG stellar mass through merging. The presence of significant amounts of stellar light at large radii from these BCGs may help towards solving the recent disagreement between the semi-analytic model predictions of BCG mass growth (e.g. De Lucia & Blaziot, 2007) and the observed large masses and scale sizes reported for BCGs at high redshift.
Backreaction effects of the large scale structure on the background dynamics have been claimed to lead to a renormalization of the background dynamics that may account for the late time acceleration of the cosmic expansion. This article emphasizes that generically the averaged flow is locally anisotropic, a property that can be related to observation. Focusing on perturbation theory, the spatially averaged shear, that characterizes the anisotropy of the flow, is computed. It is shown that this shear arising from backreaction differs from a homogeneous shear: its time evolution is different and its amplitude is completely determined by the cosmological parameters and the matter power spectrum. It ranges within (2-37)% at a redshift of order 0.5 so that the isotropy of the Hubble flow may allow to constrain the backreaction approach to dark energy.
The presence of a dark matter core in the central kiloparsec of many dwarf galaxies has been a long standing problem in galaxy formation theories based on the standard cold dark matter paradigm. Recent cosmological simulations, based on Smooth Particle Hydrodynamics and rather strong feedback recipes have shown that it was indeed possible to form extended dark matter cores using baryonic processes related to a more realistic treatment of the interstellar medium. Using adaptive mesh refinement, together with a new, stronger supernovae feedback scheme that we have recently implemented in the RAMSES code, we show that it is also possible to form a prominent dark matter core within the well-controlled framework of an isolated, initially cuspy, 10 billion solar masses dark matter halo. Although our numerical experiment is idealized, it allows a clean and unambiguous identification of the dark matter core formation process. Our dark matter inner profile is well fitted by a pseudo-isothermal profile with a core radius of 800 pc. The core formation mechanism is consistent with the one proposed by Pontzen & Governato (2012). We highlight two key observational predictions of all simulations that find cusp-core transformations: (i) a bursty star formation history with peak to trough ratio of 5 to 10 and a duty cycle comparable to the local dynamical time; and (ii) a stellar distribution that is hot with v/sigma=1. We compare the observational properties of our model galaxy with recent measurements of the isolated dwarf WLM. We show that the spatial and kinematical distribution of stars and HI gas are in striking agreement with observations, supporting the fundamental role played by stellar feedback in shaping both the stellar and dark matter distribution.
The identification of strong gravitational lenses in large surveys has historically been a rather time consuming exercise. Early data from the Herschel Astrophysical Terahertz Large Area Survey (Herschel-ATLAS) demonstrate that lenses can be identified efficiently at submillimetre wavelengths using a simple flux criteria. Motivated by that development, this work considers the statistical properties of strong gravitational lens systems which have been, and will be, found by the Herschel-ATLAS. Analytical models of lens statistics are tested with the current best estimates for the various model ingredients. These include the cosmological parameters, the mass function and the lens density profile, for which we consider the singular isothermal sphere (SIS) and the Navarro, Frenk & White (NFW) approximations. The five lenses identified in the Herschel-ATLAS Science Demonstration Phase suggest a SIS density profile is preferred, but cannot yet constrain \Omega_\Lambda to an accuracy comparable with other methods. The complete Herschel-ATLAS data set should be sufficient to yield competitive constraints on \Omega_\Lambda. Whilst this huge number of lenses has great potential for constraining cosmological parameters, they will be most powerful in constraining uncertainty in astrophysical processes. Further investigation is needed to fully exploit this unprecedented data set.
The Cosmic Infrared Background (CIB) provides an opportunity to constrain many properties of the high redshift (z>6) stellar population as a whole. This background, specifically, from 1 to 200 microns, will contain any information about the era of reionization and the stars responsible for producing these ionizing photons. In this paper, we look at the fractional anisotropy delta I/I of this high redshift population, which is the ratio of the magnitude of the fluctuations (delta I) and the mean intensity (I). We show that this can be used to constrain the escape fraction of the population as a whole. The magnitude of the fluctuations of the CIB depend on the escape fraction, while the mean intensity does not. This results in lower values of the escape fraction producing higher values of the fractional anisotropy. This difference is predicted to be larger at the longer wavelengths bands (above 10 microns), albeit it is also much harder to observe in that range. We show that the fractional anisotropy can also be used to separate a dusty from a dust-free population. Finally, we discuss the constraints provided by current observations on the CIB fractional anisotropy.
We study the redshift distribution of two samples of early-type gravitational lenses, extracted from a larger collection of 122 systems, to constrain the cosmological constant in the LCDM model and the parameters of a set of alternative dark energy models (XCDM, Dvali-Gabadadze-Porrati and Ricci dark energy models), under a spatially flat universe. The likelihood is maximized for $\Omega_\Lambda= 0.70 \pm 0.09$ when considering the sample excluding the SLACS systems (known to be biased towards large image-separation lenses) and no-evolution, and $\Omega_\Lambda= 0.81\pm 0.05$ when limiting to gravitational lenses with image separation larger than 2" and no-evolution. In both cases, results accounting for galaxy evolution are consistent within 1$\sigma$. The present test supports the accelerated expansion, by excluding the null-hypothesis (i.e., $\Omega_\Lambda = 0 $) at more than 4$\sigma$, regardless of the chosen sample and assumptions on the galaxy evolution. A comparison between competitive world models is performed by means of the Bayesian information criterion. This shows that the simplest cosmological constant model - that has only one free parameter - is still preferred by the available data on the redshift distribution of gravitational lenses. We perform an analysis of the possible systematic effects, finding that the systematic errors due to sample incompleteness, galaxy evolution and model uncertainties approximately equal the statistical errors, with present-day data. We find that the largest sources of systemic errors are the dynamical normalization and the high-velocity cut-off factor, followed by the faint-end slope of the velocity dispersion function.
We study the properties of low-velocity material in the line of sight towards
nearby Type Ia Supernovae (SNe Ia) that have measured late phase nebular
velocity shifts (v_neb), thought to be an environment-independent observable.
We have found that the distribution of equivalent widths of narrow blended Na I
D1 & D2 and Ca II H & K absorption lines differs significantly between those
SNe Ia with negative and positive v_neb, with generally stronger absorption for
SNe Ia with v_neb > 0. A similar result had been found previously for the
distribution of colors of SNe Ia, which was interpreted as a dependence of the
temperature of the ejecta with viewing angle. Our work suggests that: 1) a
significant part of these differences in color should be attributed to
extinction, 2) this extinction is caused by an asymmetric distribution of
circumstellar material (CSM) and 3) the CSM absorption is generally stronger on
the side of the ejecta opposite to where the ignition occurs.
Since it is difficult to explain 3) via any known physical processes that
occur before explosion, we argue that the asymmetry of the CSM is originated
after explosion by a stronger ionizing flux on the side of the ejecta where
ignition occurs, probably due to a stronger shock breakout and/or more exposed
radioactive material on one side of the ejecta. This result has important
implications for both progenitor and explosion models.
We have developed and characterized an imaging instrument to measure the spatial properties of the diffuse near-infrared extragalactic background light in a search for fluctuations from z > 6 galaxies during the epoch of reionization. The instrument is part of the Cosmic Infrared Background Experiment (CIBER), designed to observe the extragalactic background light above the Earth's atmosphere during a suborbital sounding rocket flight. The imaging instrument incorporates a 2x2 degree field of view, to measure fluctuations over the predicted peak of the spatial power spectrum at 10 arcminutes, and 7"x7" pixels, to remove lower redshift galaxies to a depth sufficient to reduce the low-redshift galaxy clustering foreground below instrumental sensitivity. The imaging instrument employs two cameras with \Delta \lambda / \lambda ~0.5 bandpasses centered at 1.1 and 1.6 microns to spectrally discriminate reionization extragalactic background fluctuations from local foreground fluctuations. CIBER operates at wavelengths where the electromagnetic spectrum of the reionization extragalactic background is thought to peak, and complements fluctuations measurements by AKARI and Spitzer at longer wavelengths. We have characterized the instrument in the laboratory, including measurements of the sensitivity, flat-field response, stray light performance, and noise properties. Several modifications were made to the instrument following a first flight in 2009 February. The instrument performed to specifications in subsequent flights in 2010 July and 2012 March, and the scientific data are now being analyzed.
We study the relation between the measured anisotropies in the extragalactic diffuse gamma-ray background (DGRB) and the DGRB spectral intensity, and their potential origin from the unresolved blazar population. Using a physical-evolution model for blazars with a luminosity dependent density evolution (LDDE) and an observationally-determined luminosity-dependent blazar spectral energy distribution (SED), we find that blazars can account for the observed anisotropy of the DGRB consistent with their observed source-count distribution, but are in turn constrained in contributing significantly to the observed DGRB intensity. For the best-fit LDDE model accounting for the DGRB anisotropy and source-count distribution, blazars only contribute 4.3^{+4.1}_{-1.1}% (68% CL) of the DGRB intensity above 1 GeV. Requiring a higher fraction of the DGRB intensity contribution by blazars overproduces the DGRB anisotropy, and therefore blazars in the LDDE+SED-sequence model cannot simultaneously account for the DGRB intensity as well as anisotropy. We discuss the limitations of LDDE models. However, these models do not require the many unjustified and observationally-inconsistent simplifying assumptions---including a single power law for all blazar spectra and a simple broken power-law model for their source-count distribution---that are present in much previous work.
Recently, a tentative 130 GeV $\gamma$-ray line signal was identified by quite a few groups. If correct it would constitute a "smoking gun" for dark matter annihilations. Interestingly, the spectra of the sum of cosmic ray electrons and positrons detected by ATIC and PAMELA both show small wiggle-like structure at $\sim 100$ GeV, which could be the result of the annihilation of $\sim 140$ GeV dark matter particles into electrons/positrons with a velocity-weighted cross section $<\sigma v>_{\rm \chi\chi\rightarrow e^{+}e^{-}}\sim 10^{-26}-10^{-25} {\rm cm^{3} s^{-1}}$. Accurate measurements of the total spectrum of electron and positron cosmic rays by AMS-2 and the upcoming missions such as DAMPE and CALET are highly needed to pin down the profile of the wiggle-like structure and then its physical origin.
We recently proposed a chameleonic solution to the cosmological constant problem - Phys. Rev. D82 (2010) 044006. We further elaborate on our proposal discussing also some new results. The basic ingredients of the model are A) a chameleonic string dilaton parametrizing the amount of scale symmetry of the problem in the Einstein frame; B) a dual nature of the concept of particle where a splitting in local and global components is introduced (for every local particle a corresponding global particle is present in the theory). In this paper we proceed stepwise: 1) we point out that the value of the chameleonic dilaton in the Einstein frame parametrizes also the string length and, in particular, the string mass is an increasing function of the matter density; 2) the concept of global particle is clarified (indeed global particles are simply cosmic strings); 3) in the last quantization step, in the Feynman diagrams of our model, the UV cut-off (which is chosen to be the string mass) is a function of the chameleonic dilaton (naturally this stringy regularization is fully compatible with the chameleonic scale invariance of the model); 4) we show that a large number of particle species might be useful to keep locally under control the dangerous variations of the fundamental constants, however, more research efforts are necessary to make this point clear; 5) the chameleonic behaviour of matter fields and of the de Broglie wavelength of local matter particles is pointed out; 6) we briefly touch upon some ideas (which are still waiting for a full confirmation) regarding a potential connection between the shortest length scale of nature and the cosmological constant. A detailed phenomenological analysis of the entire model is required to test these ideas.
In this paper we discuss the restrictions of the spacetime for the standard model of cosmology by using results of the differential topology of 3- and 4-manifolds. The smoothness of the cosmic evolution is the strongest restriction. The Poincare model (dodecaeder model), the Picard horn and the 3-torus are ruled out by the restrictions but a sum of two Poincare spheres is allowed.
We discuss the Hamiltonian dynamics for cosmologies coming from Extended Theories of Gravity. In particular, minisuperspace models are taken into account searching for Noether symmetries. The existence of conserved quantities gives selection rule to recover classical behaviors in cosmic evolution according to the so called Hartle criterion, that allows to select correlated regions in the configuration space of dynamical variables. We show that such a statement works for general classes of Extended Theories of Gravity and is conformally preserved. Furthermore, the presence of Noether symmetries allows a straightforward classification of singularities that represent the points where the symmetry is broken. Examples of nonminimally coupled and higher-order models are discussed.
J1211+743 is a giant radio galaxy with a one-sided jet and two asymmetric lobes, one of which is of Fanaroff-Riley (FR) type II with a hotspot and the other is a diffuse relic devoid of a hotspot. The jet points towards the latter lobe, which is difficult to explain in a standard way within the double-lobed radio source paradigm. Here, I propose to assume that the nucleus of J1211+743 has undergone a re-ignition of activity and its lobes, presumably both originally of FR II type, represent an earlier active phase, while the jet represents the current one. The asymmetry of the lobes is a consequence of the orientation of the source combined with an activity switch-off that occurred between two active periods. The relic lobe is on the near side with regard to the observer, whereas the radiation from the far-side lobe arrives significantly later owing to its longer distance to the observer. The far-side lobe is thus perceived to have not yet decayed. On the other hand, the jet behaves in a standard way, i.e. its projected orientation reflects the near side of the source. Hence, we are able to explain why the location of the relic lobe correlates with the direction of the jet.
We use high (0."65 x 0."52,(65x52pc)) resolution SubMillimeter Array (SMA)
observations to image the CO and 13CO 2-1 line emission of the extreme
FIR-excess galaxy NGC 1377. We find bright, complex CO 2-1 line emission in the
inner 400 pc of the galaxy. The CO 2-1 line has wings that are tracing a
kinematical component which appears perpendicular to that of the line core.
Together with an intriguing X-shape of the integrated intensity and dispersion
maps, this suggests that the molecular emission of NGC 1377 consists of a
disk-outflow system. Lower limits to the molecular mass and outflow rate are
M_out(H2)>1e7 Msun and dM/dt>8 Msun/yr. The age of the proposed outflow is
estimated to 1.4Myrs, the extent to 200pc and the outflow speed to 140 km/s.
The total molecular mass in the SMA map is estimated to M_tot(H2)=1.5e8 Msun
(on a scale of 400 pc) while in the inner r=29 pc the molecular mass is
M_core(H2)=1.7e7 Msun with a corresponding H2 column density of N(H2)=3.4e23
cm-2 and an average CO 2-1 brightness temperature of 19K.
Observing the molecular properties of the FIR-excess galaxy NGC 1377 allows
us to probe the early stages of nuclear activity and the onset of feedback in
active galaxies. The age of the outflow supports the notion that the current
nuclear activity is young - a few Myrs. The outflow may be powered by radiation
pressure from a compact, dust enshrouded nucleus, but other driving mechanisms
are possible. The buried source may be an AGN or an extremely young (1Myr)
compact starburst. Limitations on size and mass lead us to favour the AGN
scenario, but further studies are required to settle the issue. In either case,
the wind with its implied mass outflow rate will quench the nuclear power
source within a very short time of 5-25 Myrs. It is however possible that the
gas is unable to escape the galaxy and may eventually fall back onto NGC 1377
again.
One possible interpretation of the holographic principle is the equality of the number of degrees of freedom in a bulk region of space and the number of degrees of freedom on the boundary surface. It is known that such an equality is maintained on equipotential surfaces in any static spacetime in the form of an equipartition law N_{bulk}= N_{sur}. In the cosmological context, the de Sitter universe obeys the same holographic equipartition. I argue that the difference between the surface degrees of freedom and the bulk degrees of freedom in a region of space (which has already emerged) drives the accelerated expansion of the universe through a simple equation dV/dt = (N_{sur} - N_{bulk}) where V is the Hubble volume in Planck units and t is the cosmic time in Planck units. This equation reproduces the standard evolution of the universe. This approach provides a novel paradigm to study the emergence of space and cosmology and has far reaching implications.
A variation of sneutrino inflation based on chi^2 potential is considered where the inflaton and the late-decaying field are sneutrinos of different generations. The lighter, late-decaying sneutrino dilutes the gravitinos over-produced after inflaton decay and generates the matter asymmetry. It can also significantly contribute to the curvature perturbation, realizing the mixed inflaton-curvaton case. The cosmic microwave background (CMB) observables can distinguish this case from inflation with chi^2 potential provided that the initial value of the late-decaying sneutrino is either an order of magnitude smaller or larger than the reduced Planck scale.
We describe approximate axisymmetric computations of the dynamical evolution of material inside radio lobes and X-ray cluster gas cavities in Fanaroff-Riley II sources such as Cygnus A. All energy is delivered by a jet to the lobe/cavity via a moving hotspot where jet energy dissipates in a reverse shock. Our calculations describe the evolution of hot plasma, cosmic rays (CRs) and toroidal magnetic fields flowing from the hotspot into the cavity. Many observed features are explained. Gas, CRs and field flow back along the cavity surface in a "boundary backflow" consistent with detailed FRII observations. Computed ages of backflowing CRs are consistent with observed radio-synchrotron age variations only if shear instabilities in the boundary backflow are damped and we assume this is done with viscosity of unknown origin. Magnetic fields estimated from synchrotron self-Compton (SSC) X-radiation observed near the hotspot evolve into radio lobe fields. Computed profiles of radio synchrotron lobe emission perpendicular to the jet are dramatically limb-brightened in excellent agreement with FRII observations although computed lobe fields exceed those observed. Strong winds flowing from hotspots naturally create kpc-sized spatial offsets between hotspot inverse Compton (IC-CMB) X-ray emission and radio synchrotron emission that peaks 1-2 kpc ahead where the field increases due to wind compression. In our computed version of Cygnus A, nonthermal X-ray emission increases from the hotspot (some IC-CMB, mostly SSC) toward the offset radio synchrotron peak (mostly SSC). A faint thermal jet along the symmetry axis may be responsible for redirecting the Cygnus A non-thermal jet.
Links to: arXiv, form interface, find, astro-ph, recent, 1206, contact, help (Access key information)